I have 3 of these phones hooked up. All were working until I changed my subnet mask on my firewall from 255.255.255.0 to 255.255.240.0
This is strange, all devices have the new subnet mask, and from what I can tell so does the PBX. The devices can get their TFTP information from the server upon factory reset. They can make and recieve calls. No audio either way, drops after 30 seconds. Echo test works on softphone and on phone number calling in to DISA.
In Asterisk SIP Settings, confirm that External Address and Local Networks are correctly set. If you change these, after Submit and Apply Config you must restart Asterisk.
If that’s not your issue, at the Asterisk command prompt type pjsip set logger on
or (if the extensions are chan_sip) sip set debug on
make a failing call to *65 (speak extension number), paste the Asterisk log for the call at pastebin.freepbx.org and post the link here.