Has anyone found a replacement for the TeleMatrix DC550 feature phone for the Phonesuite PBX?

There is one. PM sent.

I have not tried it, but in the past I have heard that the old Nortel Centrex phones could be used. Also, for what it is worth, the recommendation of just using a multi-line telephone seems to be easier, especially since the feature phones were a bit pricey and the cards took a lot of space. We did that at a few properties and they were happy. We used Aastra two line telephones for the admin extensions. This also gets around the limited amount of Feature Phones that are programmable per system.