Is there any real difference between IP phones that are SIP2.0 or IAX2 compliant?
Is there any quality difference in the voice?
Easy to interface with say 20-40 phones?
Please tell me the pro’s and cons as we are seriously looking into Asterisk and digium products…
Thank you 
IAX is the way to go if you are (or could be) shooting signals thru any firewalls. It’s easier in my opinion to set firewalls for the IAX phones.
Not sure about signal quality as I gave up trying to set up my SIP as soon as I got my IAX working.
voice quality should be the same (depending on phone design of course) between iax and sip. iax is easier to deal with firewalls.
if you go sip, aastra and snom both make great phones that are pretty easy to bulk deploy…