How to improve IVR software?

Hello,

Could anyone help me corresponding to a sample software. My problem is I do not know how to start developing this sample source code, you can find below. This sample software is an IVR DTMF sample. You can find the source code of it here:
http://voip-sip-sdk.com/p_117-how-to-use-the-c-sip-softphone-source-implementation-of-ozeki-voip-sdk-for-dtmf-ivr-voip.html

Thanks for helping me!