EX-10.4: SUBSIDIARY GUARANTY

Exhibit 10.4

SUBSIDIARIES GUARANTY

among

CERTAIN SUBSIDIARIES OF RCN CORPORATION

and

DEUTSCHE BANK TRUST COMPANY AMERICAS,
as COLLATERAL AGENT

Dated as of May 25, 2007

SUBSIDIARIES GUARANTY

          SUBSIDIARIES GUARANTY (as amended, modified, restated and/or supplemented from time to time, this “ Guaranty ”), dated as of May 25, 2007, made by and among each of the undersigned guarantors (each, a “ Guarantor ” and, together with any other entity that becomes a guarantor hereunder pursuant to Section 22 hereof, collectively, the “ Guarantors ”) in favor of Deutsche Bank Trust Company Americas, as Administrative Agent (together with any successor administrative agent, the “ Administrative Agent ”), for the benefit of the Secured Creditors (as defined below). Except as otherwise defined herein, all capitalized terms used herein and defined in the Credit Agreement (as defined below) shall be used herein as therein defined.

W I T N E S S E T H :

          WHEREAS, RCN Corporation (the “ Borrower ”), the lenders from time to time party thereto (the “ Lenders ”), and the Administrative Agent, have entered into a Credit Agreement, dated as of May 25, 2007 (as amended, modified, restated and/or supplemented from time to time, the “ Credit Agreement ”), providing for the making of Loans to, and the issuance of, and participation in, Letters of Credit for the account of the Borrower, all as contemplated therein (the Lenders, each Issuing Lender, the Administrative Agent, the Collateral Agent, each other Agent and the Pledgee are herein called the “ Lender Creditors ”);

          WHEREAS, the Borrower and/or one or more of its Subsidiaries may at any time and from time to time enter into one or more Interest Rate Protection Agreements and/or Other Hedging Agreements with one or more Lenders or any affiliate thereof (each such Lender or affiliate, even if the respective Lender subsequently ceases to be a Lender under the Credit Agreement for any reason, together with such Lender’s or affiliate’s successors and assigns, if any, collectively, the “ Other Creditors ” and, together with the Lender Creditors, the “ Secured Creditors ”);

          WHEREAS, each Guarantor is a direct or indirect Subsidiary of the Borrower;

          WHEREAS, it is a condition precedent to the making of Loans to the Borrower and the issuance of, and participation in, Letters of Credit for the account of the Borrower under the Credit Agreement and to the Other Creditors entering into Interest Rate Protection Agreements and Other Hedging Agreements that each Guarantor shall have executed and delivered to the Administrative Agent this Guaranty;

          WHEREAS, each Guarantor will obtain benefits from the incurrence of Loans by the Borrower and the issuance of, and participation in, Letters of Credit for the account of the Borrower under the Credit Agreement and the entering into by the Borrower and/or one or more of its Subsidiaries of Interest Rate Protection Agreements or Other Hedging Agreements and, accordingly, desires to execute this Guaranty in order to satisfy the condition described in the preceding paragraph and to induce the Lenders to make Loans to the Borrower and issue, and/or

participate in, Letters of Credit for the account of the Borrower and the Other Creditors to enter into Interest Rate Protection Agreements or Other Hedging Agreements with the Borrower and/or one or more of its Subsidiaries; and

          WHEREAS, each Guarantor has determined that the guaranties provided in this Guaranty are necessary or convenient to the conduct, promotion or attainment of the business of the Borrower, such Guarantor and the other Guarantors, may reasonably be expected to benefit, directly or indirectly, such Guarantor, and are in the best interests of such Guarantor;

          NOW, THEREFORE, in consideration of the foregoing and other benefits accruing to each Guarantor, the receipt and sufficiency of which are hereby acknowledged, each Guarantor hereby makes the following representations and warranties to the Administrative Agent for the benefit of the Secured Creditors and hereby covenants and agrees with each other Guarantor and the Administrative Agent for the benefit of the Secured Creditors as follows:

          1. GUARANTY . (a) Each Guarantor, jointly and severally, irrevocably, absolutely and unconditionally guarantees:

     (i) to the Lender Creditors the full and prompt payment when due (whether at the stated maturity, by required prepayment, declaration, acceleration, demand or otherwise) of (x) the principal of, premium, if any, and interest on the Notes issued by, and the Loans made to, the Borrower under the Credit Agreement, and all reimbursement obligations and Unpaid Drawings with respect to Letters of Credit and (y) all other obligations (including, without limitation, obligations which, but for the automatic stay under Section 362(a) of the Bankruptcy Code, would become due), liabilities and indebtedness owing by the Borrower to the Lender Creditors under the Credit Agreement and each other Credit Document to which the Borrower is a party (including, without limitation, indemnities, Fees and interest thereon (including, without limitation, any interest accruing after the commencement of any bankruptcy, insolvency, receivership or similar proceeding at the rate provided for in the Credit Agreement, whether or not such interest is an allowed claim in any such proceeding)), whether now existing or hereafter incurred under, arising out of or in connection with the Credit Agreement and any such other Credit Document and the due performance and compliance by the Borrower with all of the terms, conditions, covenants and agreements contained in all such Credit Documents (all such principal, premium, interest, liabilities, indebtedness and obligations under this clause (i), except to the extent consisting of obligations or liabilities with respect to Interest Rate Protection Agreements or Other Hedging Agreements, being herein collectively called the “ Credit Document Obligations ”); and

     (ii) to each Other Creditor the full and prompt payment when due (whether at the stated maturity, by required prepayment, declaration, acceleration, demand or otherwise) of all obligations (including, without limitation, obligations which, but for the automatic stay under Section 362(a) of the Bankruptcy Code, would become due), liabilities and indebtedness (including, without limitation, any interest accruing after the commencement of any bankruptcy, insolvency, receivership or similar proceeding at the rate provided for in the respective Interest Rate Protection Agreements or Other Hedging

Agreements, whether or not such interest is an allowed claim in any such proceeding) owing by the Borrower and/or any other Guaranteed Party (as defined below) under any Interest Rate Protection Agreement and any Other Hedging Agreement to which it is a party, whether now in existence or hereafter arising, and the due performance and compliance by the Borrower and each such other Guaranteed Party with all of the terms, conditions, covenants and agreements contained therein (all such obligations, liabilities and indebtedness being herein collectively called the “ Other Obligations ”, and together with the Credit Document Obligations are herein collectively called the “ Guaranteed Obligations ”);

          As used herein, the term “ Guaranteed Party ” shall mean the Borrower and each Subsidiary of the Borrower party to any Interest Rate Protection Agreement or Other Hedging Agreement with an Other Creditor. Each Guarantor understands, agrees and confirms that the Secured Creditors may enforce this Guaranty up to the full amount of the Guaranteed Obligations against such Guarantor without proceeding against any other Guarantor, the Borrower or any other Guaranteed Party, or against any security for the Guaranteed Obligations, or under any other guaranty covering all or a portion of the Guaranteed Obligations. This Guaranty is a guaranty of prompt payment and performance and not of collection.

          (b) Additionally, each Guarantor, jointly and severally, unconditionally, absolutely and irrevocably, guarantees the payment of any and all Guaranteed Obligations whether or not due or payable by the Borrower or any other Guaranteed Party upon the occurrence in respect of the Borrower or any other Guaranteed Party of any of the events specified in Section 10.05 of the Credit Agreement, and unconditionally, absolutely and irrevocably, jointly and severally, promises to pay such Guaranteed Obligations to the Secured Creditors, or order, on demand.

          2. LIABILITY OF GUARANTORS ABSOLUTE . The liability of each Guarantor hereunder is absolute, joint and several, and unconditional and is exclusive and independent of any security for or other guaranty of the indebtedness of the Borrower or any other Guaranteed Party whether executed by such Guarantor, any other Guarantor, any other guarantor or by any other party, and the liability of each Guarantor hereunder shall not be affected or impaired by any circumstance or occurrence whatsoever, including, without limitation: (a) any direction as to application of payment by the Borrower, any other Guaranteed Party or any other party, (b) any other continuing or other guaranty, undertaking or maximum liability of a Guarantor or of any other party as to the Guaranteed Obligations, (c) any payment on or in reduction of any such other guaranty or undertaking, (d) any dissolution, termination or increase, decrease or change in personnel by the Borrower or any other Guaranteed Party, (e) the failure of the Guarantor to receive any benefit from or as a result of its execution, delivery and performance of this Guaranty, (f) any payment made to any Secured Creditor on the indebtedness which any Secured Creditor repays the Borrower or any other Guaranteed Party pursuant to court order in any bankruptcy, reorganization, arrangement, moratorium or other debtor relief proceeding, and each Guarantor waives any right to the deferral or modification of its obligations hereunder by reason of any such proceeding, (g) any action or inaction by the Secured Creditors as contemplated in Section 5 hereof or (h) any invalidity, rescission,

irregularity or unenforceability of all or any part of the Guaranteed Obligations or of any security therefor.

          3. OBLIGATIONS OF GUARANTORS INDEPENDENT . The obligations of each Guarantor hereunder are independent of the obligations of any other Guarantor, any other guarantor, the Borrower or any other Guaranteed Party, and a separate action or actions may be brought and prosecuted against each Guarantor whether or not action is brought against any other Guarantor, any other guarantor, the Borrower or any other Guaranteed Party and whether or not any other Guarantor, any other guarantor, the Borrower or any other Guaranteed Party be joined in any such action or actions. Each Guarantor waives (to the fullest extent permitted by applicable law) the benefits of any statute of limitations affecting its liability hereunder or the enforcement thereof. Any payment by the Borrower or any other Guaranteed Party or other circumstance which operates to toll any statute of limitations as to the Borrower or such other Guaranteed Party shall operate to toll the statute of limitations as to each Guarantor.

          4. WAIVERS BY GUARANTORS . (a) Each Guarantor hereby waives (to the fullest extent permitted by applicable law) notice of acceptance of this Guaranty and notice of the existence, creation or incurrence of any new or additional liability to which it may apply, and waives promptness, diligence, presentment, demand of payment, demand for performance, protest, notice of dishonor or nonpayment of any such liabilities, suit or taking of other action by the Administrative Agent or any other Secured Creditor against, and any other notice to, any party liable thereon (including such Guarantor, any other Guarantor, any other guarantor, the Borrower or any other Guaranteed Party) and each Guarantor further hereby waives any and all notice of the creation, renewal, extension or accrual of any of the Guaranteed Obligations and notice or proof of reliance by any Secured Creditor upon this Guaranty, and the Guaranteed Obligations shall conclusively be deemed to have been created, contracted or incurred, or renewed, extended, amended, modified, supplemented or waived, in reliance upon this Guaranty.

          (b) Each Guarantor waives any right to require the Secured Creditors to: (i) proceed against the Borrower, any other Guaranteed Party, any other Guarantor, any other guarantor of the Guaranteed Obligations or any other party; (ii) proceed against or exhaust any security held from the Borrower, any other Guaranteed Party, any other Guarantor, any other guarantor of the Guaranteed Obligations or any other party; or (iii) pursue any other remedy in the Secured Creditors’ power whatsoever. Each Guarantor waives any defense based on or arising out of any defense of the Borrower, any other Guaranteed Party, any other Guarantor, any other guarantor of the Guaranteed Obligations or any other party other than payment in full in cash of the Guaranteed Obligations, including, without limitation, any defense based on or arising out of the disability of the Borrower, any other Guaranteed Party, any other Guarantor, any other guarantor of the Guaranteed Obligations or any other party, or the unenforceability of the Guaranteed Obligations or any part thereof from any cause, or the cessation from any cause of the liability of the Borrower or any other Guaranteed Party other than payment in full in cash of the Guaranteed Obligations. The Secured Creditors may, at their election, foreclose on any collateral serving as security held by the Administrative Agent, the Collateral Agent or the other Secured Creditors by one or more judicial or nonjudicial sales, whether or not every aspect of any such sale is commercially reasonable (to the extent such sale is permitted by applicable law), or exercise any other right or remedy the Secured Creditors may have against the Borrower, any

other Guaranteed Party or any other party, or any security, without affecting or impairing in any way the liability of any Guarantor hereunder except to the extent the Guaranteed Obligations have been paid in full in cash. Each Guarantor waives any defense arising out of any such election by the Secured Creditors, even though such election operates to impair or extinguish any right of reimbursement, contribution, indemnification or subrogation or other right or remedy of such Guarantor against the Borrower, any other Guaranteed Party, any other guarantor of the Guaranteed Obligations or any other party or any security.

          (c) Each Guarantor has knowledge and assumes all responsibility for being and keeping itself informed of the Borrower’s, each other Guaranteed Party’s and each other Guarantor’s financial condition, affairs and assets, and of all other circumstances bearing upon the risk of nonpayment of the Guaranteed Obligations and the nature, scope and extent of the risks which such Guarantor assumes and incurs hereunder, and has adequate means to obtain from the Borrower, each other Guaranteed Party and each other Guarantor on an ongoing basis information relating thereto and the Borrower’s, each other Guaranteed Party’s and each other Guarantor’s ability to pay and perform its respective Guaranteed Obligations, and agrees to assume the responsibility for keeping, and to keep, so informed for so long as this Guaranty is in effect. Each Guarantor acknowledges and agrees that (x) the Secured Creditors shall have no obligation to investigate the financial condition or affairs of the Borrower, any other Guaranteed Party or any other Guarantor for the benefit of such Guarantor nor to advise such Guarantor of any fact respecting, or any change in, the financial condition, assets or affairs of the Borrower, any other Guaranteed Party or any other Guarantor that might become known to any Secured Creditor at any time, whether or not such Secured Creditor knows or believes or has reason to know or believe that any such fact or change is unknown to such Guarantor, or might (or does) increase the risk of such Guarantor as guarantor hereunder, or might (or would) affect the willingness of such Guarantor to continue as a guarantor of the Guaranteed Obligations hereunder and (y) the Secured Creditors shall have no duty to advise any Guarantor of information known to them regarding any of the aforementioned circumstances or risks.

          (d) Each Guarantor hereby acknowledges and agrees that no Secured Creditor nor any other Person shall be under any obligation (a) to marshal any assets in favor of the Guarantor or in payment of any or all of the liabilities of any Guaranteed Party under the Documents or the obligation of the Guarantor hereunder or (b) to pursue any other remedy that the Guarantor may or may not be able to pursue itself, any right to which the Guarantor hereby waives.

          (e) Each Guarantor warrants and agrees that each of the waivers set forth in Section 3 and in this Section 4 is made with full knowledge of its significance and consequences and that if any of such waivers are determined to be contrary to any applicable law or public policy, such waivers shall be effective only to the maximum extent permitted by applicable law.

          5. RIGHTS OF SECURED CREDITORS . Subject to Sections 4 and 13, any Secured Creditor may (except as shall be required by applicable statute that cannot be waived) at any time and from time to time without the consent of, or notice to, any Guarantor, without incurring responsibility to such Guarantor, without impairing or releasing the obligations or

liabilities of such Guarantor hereunder, upon or without any terms or conditions and in whole or in part:

     (a) change the manner, place or terms of payment of, and/or change, increase or extend the time of payment of, renew, increase, accelerate or alter, any of the Guaranteed Obligations (including, without limitation, any increase or decrease in the rate of interest thereon or the principal amount thereof), any security therefor, or any liability incurred directly or indirectly in respect thereof, and the guaranty herein made shall apply to the Guaranteed Obligations as so changed, extended, increased, accelerated, renewed or altered;

     (b) take and hold security for the payment of the Guaranteed Obligations and sell, exchange, release, surrender, impair, realize upon or otherwise deal with in any manner and in any order any property or other collateral by whomsoever at any time pledged or mortgaged to secure, or howsoever securing, the Guaranteed Obligations or any liabilities (including any of those hereunder) incurred directly or indirectly in respect thereof or hereof, and/or any offset thereagainst;

     (c) exercise or refrain from exercising any rights against the Borrower, any other Guaranteed Party, any other Credit Party, any Subsidiary thereof, any other guarantor of the Borrower or others or otherwise act or refrain from acting;

     (d) release or substitute any one or more endorsers, Guarantors, other guarantors, the Borrower, any other Guaranteed Party or other obligors;

     (e) settle or compromise any of the Guaranteed Obligations, any security therefor or any liability (including any of those hereunder) incurred directly or indirectly in respect thereof or hereof, and may subordinate the payment of all or any part thereof to the payment of any liability (whether due or not) of the Borrower or any other Guaranteed Party to creditors of the Borrower or such other Guaranteed Party other than the Secured Creditors;

     (f) apply any sums by whomsoever paid or howsoever realized to any liability or liabilities of the Borrower or any other Guaranteed Party to the Secured Creditors regardless of what liabilities of the Borrower or such other Guaranteed Party remain unpaid;

     (g) consent to or waive any breach of, or any act, omission or default under, any of the Interest Rate Protection Agreements or Other Hedging Agreements, the Credit Documents or any of the instruments or agreements referred to therein, or otherwise amend, modify or supplement any of the Interest Rate Protection Agreements or Other Hedging Agreements, the Credit Documents or any of such other instruments or agreements;

     (h) act or fail to act in any manner which may deprive such Guarantor of its right to subrogation against the Borrower or any other Guaranteed Party to recover full indemnity for any payments made pursuant to this Guaranty; and/or

     (i) take any other action or omit to take any other action which would, under otherwise applicable principles of common law, give rise to a legal or equitable discharge of such Guarantor from its liabilities under this Guaranty (including, without limitation, any action or omission whatsoever that might otherwise vary the risk of the Guarantor or constitute a legal or equitable defense to or discharge of the liabilities of a guarantor or surety or that might otherwise limit recourse against the Guarantor).

          No invalidity, illegality, irregularity or unenforceability of all or any part of the Guaranteed Obligations, the Credit Documents or any other agreement or instrument relating to the Guaranteed Obligations or of any security or guarantee therefor shall affect, impair or be a defense to this Guaranty, and this Guaranty shall be absolute and unconditional notwithstanding the occurrence of any event or the existence of any other circumstances which might constitute a legal or equitable discharge of a surety or guarantor except payment in full in cash of the Guaranteed Obligations.

          6. CONTINUING GUARANTY . This Guaranty is a continuing one and all liabilities to which it applies or may apply under the terms hereof shall be conclusively presumed to have been created in reliance hereon. No failure or delay on the part of any Secured Creditor in exercising any right, power or privilege hereunder shall operate as a waiver thereof, nor shall any single or partial exercise of any right, power or privilege hereunder preclude any other or further exercise thereof or the exercise of any other right, power or privilege. The rights and remedies herein expressly specified are cumulative and not exclusive of any rights or remedies which any Secured Creditor would otherwise have. No notice to or demand on any Guarantor in any case shall entitle such Guarantor to any other further notice or demand in similar or other circumstances or constitute a waiver of the rights of any Secured Creditor to any other or further action in any circumstances without notice or demand. It is not necessary for any Secured Creditor to inquire into the capacity or powers of the Borrower or any other Guaranteed Party or the officers, directors, partners or agents acting or purporting to act on its or their behalf, and any indebtedness made or created in reliance upon the professed exercise of such powers shall be guaranteed hereunder.

          7. SUBORDINATION OF INDEBTEDNESS HELD BY GUARANTORS . Any indebtedness of the Borrower or any other Guaranteed Party now or hereafter held by any Guarantor is hereby subordinated to the indebtedness of the Borr