Inquiry related to IVR

Basically I am developing an IVR application at small level with one voice modem and one pnoe line. I am in completion of the project but I am stuck at one point, that is how to convert the pulse tone to touch tone at the other end of the phone, i. e. the phone who dialed my application. At present I am developing my application using VC++ and TAPI. SO guide me in this regard.