Voice Over IP should have little or nothing to do with it.
Voice over Ip uses special phones and VOIP enabled switches to route voice calls over a "data"(IP) network.
IVR takes a voice call and interfaces it to a computer program - this can be done totally independant of how the voice call arrives at the IVR box.
The IVR systems I have seen are like fax servers in reverse - they are PCs with cards in them that attach to either digital or analogue phone lines. One would assume that using a box like that with a VOIP network would entail a special card, but you would still want analogue cards as well - as people can use IVR from their cell phone, home etc. The programming of the IVR doesn't change, just the physical interface.
Idon't have any codes - never worked on it, but had co-workers who did. Your best bet is to find out what kind of IVR system your employer has and then get the technical details about it off the web. There may be user groups for those IVR systems where they share samples.
James