CSG SYSTEMS INTERNATIONAL, INC. 2001 STOCK INCENTIVE PLAN

Exhibit 10.06

[As amended August 14, 2007,

effective as of January 1, 2005]

CSG SYSTEMS INTERNATIONAL, INC.

2001 STOCK INCENTIVE PLAN

1. Purpose. The purpose of the CSG Systems International, Inc. 2001 Stock Incentive Plan (the “Plan”) is to foster and promote the long-term financial success of the Company and its Subsidiaries and thereby increase stockholder value by providing incentives to certain key employees who are likely to be responsible for achieving such success. In furtherance of such purpose, the Plan authorizes the sale and issuance of Common Stock pursuant to sub-plans which are designed to achieve desired tax or other objectives in particular locations outside of the United States.

2. Certain Definitions.

“Board” means the Board of Directors of the Company.

“Code” means the Internal Revenue Code of 1986, as amended from time to time, or any successor thereto. References to a particular section of the Code shall include any regulations issued under such section.

“Committee” shall have the meaning provided in Section 3 of the Plan.

“Common Stock” means the Common Stock, $0.01 par value per share, of the Company.

“Company” means CSG Systems International, Inc., a Delaware corporation.

“Disability” means a mental or physical condition which, in the opinion of the Committee, renders a grantee unable or incompetent to carry out the job responsibilities which such grantee held or the tasks to which such grantee was assigned at the time the disability was incurred and which is expected to be permanent or for an indefinite duration exceeding one year.

“Exchange Act” means the Securities Exchange Act of 1934, as amended from time to time.

“Fair Market Value” means, as determined by the Committee, the last sale price of the Common Stock as quoted on the Nasdaq National Market System on the trading day for which the determination is being made, or, in the event that no such sale takes place on such day, the average of the reported closing bid and asked prices on such day, or, if the Common Stock of the Company is listed on a national securities exchange, the last reported sale price on the principal national securities exchange on which the Common Stock is listed or admitted to trading on the trading day for which the determination is being made, or, if no such reported sale takes place on such day, the average of the closing bid and asked prices on such day on the principal national securities exchange on which the Common Stock is listed or admitted to trading, or, if the Common Stock is not quoted on such National Market System nor listed or admitted to trading on a national securities exchange, the average of the closing bid and asked prices in the over-the-counter market

on the day for which the determination is being made as reported through Nasdaq, or, if bid and asked prices for the Common Stock on such day are not reported through Nasdaq, the average of the bid and asked prices for such day as furnished by any New York Stock Exchange member firm regularly making a market in the Common Stock selected for such purpose by the Committee, or, if none of the foregoing is applicable, then the fair market value of the Common Stock as determined in good faith by the Committee in its sole discretion.

“Parent Corporation” means any corporation (other than the Company) in an unbroken chain of corporations ending with the Company if, at the time of the granting of the option, each of the corporations other than the Company owns stock possessing 50% or more of the total combined voting power of all classes of stock in one of the other corporations in such chain.

“Performance Unit Award” means an award granted pursuant to Section 8.

“Plan Year” means the twelve-month period beginning on January 1 and ending on December 31; provided, that the first Plan Year shall be a short Plan Year beginning on the date of adoption of the Plan by the Board and ending on December 31, 2001.

“Restricted Stock Award” means an award of Common Stock granted pursuant to Section 9.

“Rule 16b-3” means Rule 16b-3 under the Exchange Act, as in effect from time to time.

“Stock Appreciation Right” means an award granted pursuant to Section 7.

“Stock Bonus Award” means an award of Common Stock granted pursuant to Section 10.

“Stock Option” means any option to purchase Common Stock granted pursuant to Section 6.

“Subsidiary” means a corporation, domestic or foreign, of which not less than 50% of the voting shares are held by the Company or by a Subsidiary, whether or not such corporation now exists or hereafter is organized or acquired by the Company or by a Subsidiary.

3. Administration. The Plan shall be administered by a committee composed solely of two or more members of the Board (the “Committee”) selected by the Board, each of whom shall qualify as a “Non-Employee Director” within the meaning of Rule 16b-3 and as an “outside director” within the meaning of Section 162(m) of the Code.

The Committee shall have authority to grant to eligible employees of the Company or its Subsidiaries, pursuant to the terms of the Plan, (a) Stock Options, (b) Stock Appreciation Rights, (c) Restricted Stock Awards, (d) Performance Unit Awards, (e) Stock Bonus Awards, or (f) any combination of the foregoing.

Subject to the applicable provisions of the Plan, the Committee shall have authority to interpret the provisions of the Plan and to decide all questions of fact arising in the application of such provisions; to select the key employees to whom awards or options shall be granted under the Plan; to determine whether and to what extent awards or options shall be granted under the Plan; to determine the types of awards and options to be granted under the Plan and the amount, size, terms, and conditions of each such award or

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option; to determine the time when awards or options shall be granted under the Plan; to determine whether, to what extent, and under what circumstances the payment of Common Stock and other amounts payable with respect to an award granted under the Plan shall be deferred either automatically or at the election of the grantee; to determine the Fair Market Value of the Common Stock from time to time; to authorize persons to execute on behalf of the Company any agreement required to be entered into under the Plan; to adopt, alter, and repeal such administrative rules, guidelines, and practices governing the Plan as the Committee from time to time shall deem advisable; and to make all other determinations necessary or advisable for the administration of the Plan.

Unless otherwise expressly provided in the Plan, all decisions and determinations made by the Committee pursuant to the provisions of the Plan shall be made in the sole discretion of the Committee and shall be final and binding on all persons, including but not limited to the Company and its Subsidiaries, the key employees to whom awards and options are granted under the Plan, the heirs and legal representatives of such key employees, and the personal representatives and beneficiaries of the estates of such key employees.

Notwithstanding any other provisions of the Plan to the contrary, the Committee may, in its sole discretion, amend or vary the terms of the Plan in order to conform such terms to the requirements of each non-U.S. jurisdiction where a Subsidiary is located or to accomplish the purpose of the Plan with respect to persons employed in such non-U.S. jurisdictions who are eligible to receive awards and options under the Plan. The Committee may, where it deems appropriate in its sole discretion, establish one or more sub-plans for such purposes; and the Committee may, in its sole discretion, establish administrative rules and procedures to facilitate the operation of the Plan or such sub-plans in such non-U.S. jurisdictions. For purposes of clarity, the terms of the Plan which will vary in a particular non-U.S. jurisdiction shall be reflected in a written addendum to the Plan for such non-U.S. jurisdiction.

The Committee may delegate to any officer or officers of the Company any of the Committee’s duties, powers, and authorities under the Plan upon such conditions and with such limitations as the Committee may determine.

4. Common Stock Subject to the Plan. Subject to adjustment pursuant to Section 19, the maximum number of shares of Common Stock which may be issued under the Plan is 3,000,000; and the Company shall reserve and keep available for issuance under the Plan such maximum number of shares, subject to adjustment pursuant to Section 19. Such shares may consist in whole or in part of authorized and unissued shares or treasury shares or any combination thereof. The aggregate number of shares of Common Stock subject to or issuable in payment of (i) Stock Options, (ii) Stock Appreciation Rights, (iii) Stock Bonus Awards, (iv) Restricted Stock Awards, or (v) Performance Unit Awards granted under the Plan in any Plan Year to any individual may not exceed 100,000, subject to adjustment pursuant to Section 19. Except as otherwise provided in the Plan, any shares subject to an option or right which expires for any reason or terminates unexercised as to such shares shall again be available for the grant of awards or options under the Plan. If any shares of Common Stock have been pledged as collateral for indebtedness incurred by an optionee in connection with the exercise of a Stock Option and such shares are returned to the Company in satisfaction of such indebtedness, then such shares shall again be available for the grant of awards or options under the Plan.

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5. Eligibility to Receive Awards and Options. Awards and options may be granted under the Plan to those key employees of the Company or any Subsidiary who are responsible for or contribute to, or are likely to be responsible for or contribute to, the management, growth and success of the Company or any Subsidiary; provided, that no award or option may be granted under the Plan to (i) any person who is an officer or director of the Company, (ii) any person who is a “covered employee” of the Company for purposes of Section 162(m) of the Code, or (iii) any person who is subject to Section 16 of the Exchange Act by reason of such person’s position with the Company or any Subsidiary, in each case at the time of the granting of the award or option. The granting of an award or option under the Plan to a key employee of the Company or any Subsidiary shall conclusively evidence the Committee’s determination that such grantee meets one or more of the criteria referred to in the preceding sentence. A director of any Subsidiary who is not an employee of the Company or any Subsidiary shall not be eligible to participate in the Plan.

6. Stock Options. Every Stock Option granted under the Plan shall be a nonqualified stock option for purposes of the Code. Stock Options may be granted alone or in addition to other awards made under the Plan. Stock Options shall be evidenced by agreements in such form as the Committee shall approve from time to time. The agreements shall contain in substance the following terms and conditions and may contain such additional terms and conditions, not inconsistent with the terms of the Plan, as the Committee shall deem appropriate:

(a) Type of Option. Each option agreement shall identify the Stock Option represented thereby as a nonqualified stock option for purposes of the Code.

(b) Option Price and Number of Shares. Each option agreement shall set forth the number of shares of Common Stock covered by the Stock Option and the applicable option exercise price per share, which price shall not be less than the Fair Market Value of the Common Stock on the date the Stock Option is granted or less than the par value of the Common Stock.

(c) Term. Each option agreement shall state the period or periods of time within which the Stock Option may be exercised, in whole or in part, which shall be such period or periods of time as the Committee may determine at the time of the Stock Option grant; provided, that no Stock Option granted under the Plan shall be exercisable more than ten years after the date of its grant; and provided further, that each Stock Option granted under the Plan shall become exercisable one year after the date of its grant, unless the option agreement specifically provides otherwise. The Committee shall have authority to accelerate previously established exercise rights, subject to the requirements set forth in the Plan, under such circumstances and upon such terms and conditions as the Committee shall deem appropriate.

(d) Payment for Shares. The Committee may permit all or part of the payment of the option exercise price to be made (i) in cash, by check or by wire transfer or (ii) in shares of Common Stock (A) which already are owned by the optionee and which are surrendered to the Company in good form for transfer or (B) which are retained by the Company from the shares of the Common Stock which would otherwise be issued to the optionee upon the optionee’s exercise of the Stock Option. Such shares shall be valued at their Fair Market Value on the date of exercise of the Stock Option. In lieu of payment in fractions of shares, payment of any fractional share amount shall be made in cash or check payable to the Company. The Committee also may

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provide that the exercise price may be paid by delivering a properly executed exercise notice in a form approved by the Committee together with irrevocable instructions to a broker to promptly deliver to the Company the amount of the applicable sale or loan proceeds required to pay the exercise price. No shares of Common Stock shall be issued to any optionee upon the exercise of a Stock Option until the Company receives full payment therefor as described above.

(e) Rights upon Termination of Employment. In the event that an optionee ceases to be employed by the Company and all of its Subsidiaries for any reason other than such optionee’s death or Disability, any rights of the optionee under any Stock Option then in effect immediately shall terminate; provided, that the optionee (or the optionee’s legal representative) shall have the right to exercise the Stock Option during its term within a period of three (3) months after such termination of employment to the extent that the Stock Option was exercisable at the time of such termination or within such other period and subject to such other terms and conditions as may be specified by the Committee. Notwithstanding the foregoing provisions of this Section 6(e), the optionee (and the optionee’s legal representative) shall not have any rights under any Stock Option, and the Company shall not be obligated to sell or deliver shares of Common Stock (or have any other obligation or liability) under any Stock Option, if the Committee shall determine that (i) the employment of the optionee with the Company or any Subsidiary has been terminated for cause or (ii) the optionee has engaged or may engage in employment or activities competitive with the Company or any Subsidiary or contrary, in the opinion of the Committee, to the best interests of the Company or any Subsidiary. In the event of such determination, the optionee (and the optionee’s legal representative) shall have no right under any Stock Option to purchase any shares of Common Stock regardless of whether the optionee (or the optionee’s legal representative) shall have delivered a notice of exercise prior to the Committee’s making of such determination. Any Stock Option may be terminated entirely by the Committee at the time of or at any time subsequent to a determination by the Committee under this Section 6(e) which has the effect of eliminating the Company’s obligation to sell or deliver shares of Common Stock under such Stock Option.

In the event that an optionee ceases to be employed by the Company and all of its Subsidiaries by reason of such optionee’s Disability, prior to the expiration of a Stock Option and without such optionee’s having fully exercised such Stock Option, such optionee or such optionee’s legal representative shall have the right to exercise such Stock Option during its term within a period of six (6) months after such termination of employment to the extent that such Stock Option was exercisable at the time of such termination or within such other period and subject to such other terms and conditions as may be specified by the Committee.

In the event that an optionee ceases to be employed by the Company and all of its Subsidiaries by reason of such optionee’s death, prior to the expiration of a Stock Option and without such optionee’s having fully exercised such Stock Option, the personal representative of such optionee’s estate or the person who acquired the right to exercise such Stock Option by bequest or inheritance from such optionee shall have the right to exercise such Stock Option during its term within a period of twelve (12) months after the date of such optionee’s death to the extent that such Stock Option was exercisable at the time of such death or within such other period and subject to such other terms and conditions as may be specified by the Committee.