I had done that for our system and working fine. I use a SIPURA made SPA2000 as two incoming analog lines. Then put SPA2000 on each of the other end. Sign up four accounts with sipphone.com, which is totally free and much faster response than FWD. Enter two sipphone accounts into the SPA2000 near the Notel. One sipphone each into the remote SPA2000s.
Set the two analog lines connected to SPA2000 as one group, I use group C. then setup routing when the two extension number being called, it actually dial the sipphone account numbers by using group C lines.
Works reliably!