I started using FreePBX with hardphones on LAN. SIP, chansip: Easy.
I moved few extensions to PJSIP to be able to use hardphone and softphone at the same time. OK. Simple. All devices are registered and ringing and can answer.
I now have users asking to use softphones on tablet and mobile from internet.
It looks simple and safer to use IAX and one single UDP port to pass through the NAT firewall.
Is it possible to use IAX2 on softphone (I did and it’s OK) but with the same extension on both the mobile and the tablet (similar to what PJSIP permits)?