> Cisco is supposed to support it with new release 12.3(7) IOS
First of all, there is no 12.3.7 IOS, there is only 12.3.6, 12.3.6a, 12.3.6b and 12.3.9. Or do you mean 12.3T IOS line?
Second, you can have an IVR on the VoIP call leg in the previous IOS versions, but only if g711 codec is used.
Where did you get your information? Perhaps you misunderstood something?