I had a “old” Freedom box with ejabberd and Coturn. A used my own domainname (123test.com) with the conversations app i send massage and i can make phone calls.
Users 1 2 3
Now i setup a new freedombox with the same domainname and ejabberd, coturn, and the same users.
New users can make phone calls but the old users 1,2,3 can send a message but not make a phone call.
Old config - PI
New config - PC debian freedombox
Please check that the ports needed for coturn (and all other ports) are getting forwarded properly from the router to FreedomBox.
If one user can make phone calls then i fink all the users can make phone calls
Depending on whether the devices have public IP addresses and based on the type of NAT they are behind, they may not need or need STUN/TURN (provided by Coturn). You can confirm this as follows: log out a new user from a working device and login an old user and try calling.