I’m trying to place outbound calls to a three digit voip extension using the gnome-calls app, but it keeps getting routed over the cellular connection. Voip account is active and will receive calls. Voip calls will route correctly when modem switch is disabled and phone is connected via Wi-Fi or Ethernet.
Is this a bug in gnome-calls or something specific to PureOS Crimson on the Librem?
Maybe related to this?
Do you hav IPv6 disabled on wifi?
I don’t believe I have IPv6 disabled. I do know that when I had IPv6 enabled with the Linphone app on another android phone, I had constant issues with outbound phone calls dropping after 30 seconds. Disabling IPv6 resolved that issue.
Still unclear exactly why IPv6 being enabled would route a three digit call dialed with voip provider selected in the gnome-calls app over the cellular provider. It seems like gnome-calls is deliberately ignoring the preference set in the app.
You have hold the phone down about 2 or 3 feet off the ground so those little Gnomes can use it.
Found an existing gnome-calls bug report for this issue, originally opened in 2022. 
Looks like the application is configured to fall back to cellular whenever there is an issue placing a call via voip. Might be a dial plan issue, perhaps a three digit number is confusing the app.