Is There a Way to Run an Open Source IVR Off of VOIP Without Using Hardware?

The IVR server would intercept VOIP calls and handle them. From what I can tell, there would be no need for hardware since it will all be done internally. The server could contain the code to convert the VOIP signal, if that is even necessary.

I have been doing searches on this but I thought I would throw it out here as well.