@thomas-k8s
If you talk about VoLTE wich work only with 4g, there is no support for it on UT for now, and VoLTE is the only dialing way with 4g so any phone that support 4g but not VoLTE, like mine, will never be able to dial in 4g.
Normally, phone should swich to 3g or 2g for dialing, like mine is doing, unless your provider force 4g and VoLTE...