I’ve been asked to research IPTelephony. Anyone offer any advice, web sites, competitors, security MCI, Cisco, Avaya?
NORTEL is a big player www.nortelnetworks.com
It is a very very broad subject with lots of players.
What exactly are you trying to research?
IP Telephony itself? Its implementation? Merits?
good sources for IP telephony basics are:
www.avaya.com and www.cisco.com
They have lots of materials on what IP telephony is and how to use it. But if you need something more concrete, I am sure would be more than happy to pitch in! 
What kind of info do you need?