Hello, my Swisscom SIM was working perfectly for many years while I'm abroad. However, after AT&T and T-mobile operators in USA have switched to 5G service and discontinued UMTS/GSM basic services (they call them 4G here), the LTE service no longer works. The phone is capable of support of required frequency bands as well as VoLTE. Data amd voice roaming are switched one, as well as VoLTE support. The SIM is capable of attaching the network, shows 5 bars of signal strength and can receive SMS and rate notifications from Swisscom. However, no Voice or data connection can be made and no SMS can be sent. The phone replies 'Connection problem or invalid MMI code' on any attempt to call, send SMS or send USSD request.
The phone is known good and works with AT&T SIM w/o any change in setup parameters. I never had a problem with SwissCom cards and have used them extensively in many countries all over the world; this was the main advantage of using SwissCom abroad - they have roaming agreements everywhere. However, after 5G rollout SwissCom cards no longer work in the US.
Anyone knows what's happening here with roaming support in general and SwissCom cards in particular? The reaction seems similar to an attempt to use black-listed phone but with ability to receive SMS messages...
Any help will be greatly appreciated. Thanks!
