Nortel has been the walking dead, its heroic and dedicated engineers like the still-vital organs struggling with weakening condition to produce and support IP-oriented quality products as they were drained with layoffs. Little wonder that in the contact center field at least, reported Interactive Intelligence's Joe Staples--whose firm has seen competitors like the 'old' Aspect, Davox, Rockwell et al disappear and many others fade into insignificance--Nortel's product line was aging with little new to get these buyers excited.
Then again IP-from-the-ground-up companies like Aastra, Cisco, Fonality, Interactive Intelligence, and ShoreTel, to name but a few, didn't have the legacy TDM/PSTN baggage to lug with them. For these companies there is no need to 'migrate' customers to IP; they are already there.