I'm having the same problem...
I have this modem: MultiTech Systems MT5634ZPX-PCI
When I had a Windows XP computer, I ran the program with this modem. It worked just fine.
I just got a new computer with Vista 64-bit. I loaded the newest version of IVM.
I uploaded the latest drivers for my modem.
With everything installed, I try to call the line. It answers and Microsoft Anna says my modem's name and says the number is unknown.
The IVM seems to answer the call, but no sound on the other end of the phone. Then it hangs up and that is it.
The Multitech technician says that the modem is working correctly with updated drivers. It is installed on COM 3.
Is there something that I haven't set up correctly?
Since I had it working on my previous computer, is there something with the Vista 64-bit that isn't compatable?