You might have missed it, but Nortel is the worldwide leader in Carrier VoIP (cf. Dell'Oro Group), having shipped 100 million IP Powered Home and IP Powered Business. ports to 320 carriers, and to two thirds of IDC's worldwide listing of top 20 carriers.
Nortel is no slouch in enterprise VoIP either, and service providers are key partners in this regard.
For example, Verizon Business has just announced that it is adding a new IP PBX platform, the Nortel CS 1000 to its portfolio. The CS 1000 SIP trunking capability has been rigorously tested and certified with Verizon Business, providing agility and improved price performance over legacy ISDN approaches.