How about making SIP the backbone of the application?
Let's talk about the future of telephony, especially in the enterprise. Telephony in the enterprise is all about SIP. Sorry, let's fix that... ALL ABOUT SIP. At this point, it's really not even up for serious discussion. Any enterprise infrastructure will probably live and die on it's ability to play well in a SIP architecture. A quick check on the Net shows some hard clients that support IAX, which I suppose is inevitable. But, the number of SIP endpoints far outweighs the number of IAX endpoints. The functionality in SIP far outweighs IAX. That's not to say that IAX doesn't do firewalls better, because it does. But IAX and SIP are fundamentally different, and SIP is fundamentally better. Any iPBX that isn't very, very SIPPY is going to lose to one that is.