benjib1980 Hi there. I reached out to the development team about this, and I think there's a potential fix.
It will include you installing Sandboxed Google Play in your owner profile. That is because Cellcom uses GSMA TS.43 provisioning.
Android 12 introduced support for the GSMA TS.43 standard where provisioning for VoLTE, VoNR and Wi-Fi calling may be handled by Google Firebase. Currently it is very rare for carriers to be using Firebase to handle this. It is unlikely, but technically possible, that with such carriers you may be required to install sandboxed Google Play in order to obtain the former mentioned functionality where the carrier has not implemented fallback provisioning via SMS. Currently only US Cellular, Orange France, Cspire US, and Cellcom US are using this standard.
If this does indeed resolve this issue for you, please let us know so that I can mark this one as solved and help others in the future!