AMENDMENT TO INVESTOR RIGHTS AGREEMENT

Exhibit 10.23.1

AMENDMENT

TO

INVESTOR RIGHTS AGREEMENT

(Dated as of April 13, 2006)

Reference is made to the INVESTOR RIGHTS AGREEMENT, dated as of August 18, 2005 (the “Investor Rights Agreement”), between DOLPHIN DIRECT EQUITY PARTNERS, LP, a Delaware limited partnership, and ACT TELECONFERENCING, INC., a Colorado corporation.

1. The parties hereto hereby amend the Investor Rights Agreement, effective as of the date hereof, as follows:

Section 2(f) of the Investor Rights Agreement is hereby amended by adding the following at the end thereof:

“Notwithstanding the foregoing, the aggregate amount of Registration Delay Payments shall not exceed an amount equal to the product of (i) the initial principal amount paid for the Series AA Preferred held by such holder or the related Conversion