@Rondarius You are right, as the Pro was happy working on VoLTE with the software shipped using VoLTE. No need to update the firmware - although an update AFAIK would allow some other networks to be used that are not supported in the original. So I attempted use phone calls at which point the phone was permanently blocked from the network. As I saw afterwards: The settings show an option to enable VoLTE - but was set to disable. Given the network permanent block have no way to test. I am aware that you can directly allow the feature in the modem - unfortunately that is too late now, this phone is now barred from the network.

Please remove disabling VoLTE by default on these phones.

Pinephone Pro and Pinephone support VoLTE as these phones have a separate chip that can handle VoLTE. It is is tested and worksed with the software shipped with the PRO, with Mobian and PostmarketOS on the PP. Installing UBPorts has disabled VoLTE. This is a problem where 3G is turned off. Even more serious where carries then block the phone, so even after restoring the original software using the phone on the mobile network is not possible. (Hard to believe, but there is a country where goverment mandated that phones not being able to use VoLTE should be blocked using the network: https://medium.com/@jamesdwho/australias-3g-shutdown-telcos-to-block-working-4g-5g-phones-2bf41e95de8a Text of regulation: https://www.legislation.gov.au/F2024L01353/asmade/text ).