Phew! Busy couple of days for me. Sorry for the late reply.
OK, so the setup is as @JaredBusch assumed. VPN on the Laptop only. Split tunneling was not enabled and now it is. Problem solved for now! DuckDNS is reporting the correct home IP. No need for VPN on the phone or PBX.
Ask your users if their kids use Steam. Most of my home users have older "kids" I tell them to have their kids stop there Steam games. The users are like what's that?? But as soon as steam is stopped their perfomance comes right back to nominal.
It would be them downloading more games, most likely.
I don't see a firmware for the T54W nor is the EXP50 available.
These phones are basically new since October or so. They will not be in EPM anytime soon because of how that has traditionally worked. The device manufacturer has to sing an agreement with Sangoma (Schmoozecom) to get a device supported. I assume, but do not know for a fact, that the agrement includes monetary compensation also, as anything in EPM is fully tested by Sangoma also, and testing takes manpower (money).
I wouldn't want it off whole sale. I could definitely do that for most users, but my phone does have a display large enough to tell me I have missed calls - and I call those people back, even if they didn't leave a message. More often than not it's beneficial to call them back and solve whatever problem they were having.