IVR support for VoIP

I am currently looking to implement an Asterisk IVR system. I am very new to Asterisk and have been talking to someone with some experience in the field. I was told that he had an Asterisk system with IVR but the IVR only functioned with E1 line traffic… any VoIP traffic had to be basically routed out of his E1/VoIP gateway and straight back in in a kind of loopback config so that IVR would work.

Is this correct? Or is there a way of configuring Asterisk IVR to work directly with voip traffic (sip or h.323) :question: