I'm comfortable with the SIP side of it, and I know that Asterisk supports that, I guess what I am asking is does the VSP also need to support IAX as well as
SIP for Asterisk to work, or is SIP on its own sufficient? You seem to be saying that SIP alone is OK.
Subsequently, I read that IAX is used between Asterisk servers (so clearly not required for what we are trying to do) but also in some client-server models (http://en.wikipedia.org/wiki/Iax
) - assuming this is from the handset to the LMCE box? And that again this is optional, and only possible if the handset (or softphone) supports IAX?
It also says that IAX provides extra functionality to your provider, like a more efficient trunking, etc. Is this something that I should think about talking to them about, or is SIP, again, enough for my purposes - just want to be able to run a couple of "lines"/numbers, voice mail, interface with the GPRS/EDGE/3G/HSDPA networks for mobile data/video calls, conferencing, call waiting, etc...