We're a long time Nortel shop, and with the Avaya takeover, have had some decent success with selling the IP Office product which has so far proven to be reliable. We've also jumped back into the Cisco market as well - along with a successful Microsoft Lync practice.
We all know sooner or later the Nortel Meridian 1, Norstar, BCM and CS1000 platforms will disappear - but we have a strong customer base on these platforms and a healthy parts supply in our warehouse.
Problem with the Norstars is they were engineered so well that they are just too reliable, but no one wants to part ways with them and upgrade to something new and shiny. I can't blame them. We've tried throwing other products aimed at the SMB sector to these customers and they won't let go of their Norstar systems.
I'm surprised at the number of BCM 200/400 systems we still have out there approaching the 10 year mark. So long as the hard drives and power supplies don't crap out - it's done well for a Windows NT based system.
Cisco is a nice product, and it will certainly supplant the lost Nortel business as time goes by - but it has it's issues to, especially when it comes to analog fax/data endpoints, LAN/WAN issues, etc. If a customer's IT department and network is not ready for it - they will feel the pain for a long time... and bill by the hour vendors such as myself will reap the benefits.
It does bug me to see customers jump quickly on the latest and greatest product because they dismiss their Nortel platform as "old technology". But I have 20 year old PBX's (especially the 61c/81c stuff) that run for years at 100% uptime so long as house/backup power to the systems is reliable... and a good number of customers with critical needs are reluctant to part ways with them so long as parts and knowledgeable techs are still around to keep them up and running.
As others have said - in recent years, the CS1000's, as nice as they are - just aren't as reliable as the Meridian product. Patching / updating software on co-res Linux based systems takes hours... meaning long downtime for customers. I mean really?
And don't get me started with the buggy phone system software Nortel has put out - but those are more for the customer's, not techs (Telephony Manager - just awful).
For me, I'm in a Nortel to Cisco transition period. This change is inevitable as there's no future in 20 year old technology. There's some job security by obscurity as the older Nortel trained guys retire and I pick up their workload... but that's just a short-term strategy until our Cisco customer base outnumbers the Nortel base.