Linphone supports ICE and therefore it should work more reliably behind NAT than some of the other softphones.

It receives calls from Lumicall users.

Complete the setup wizard

wizard-1.png

wizard-2.png

wizard-3-1-proxy.png

Add some settings manually

Select TLS, select ICE and put in the STUN/TURN server name turn.debian.org

settings-1-network.png

settings-2-sip-account-details.png

settings-2-sip-accounts.png

settings-3-ui-advanced.png

Authentication popup

The first time it tries to connect to the SIP proxy, it will complain about authentication.

This is because you have to add @debian.org to the authentication username:

auth-dialog-highlight.png

It should remember that and will not prompt again.