It seems you are correct. The question is, why? If this is a policy intended to boost the sales of T-Mobile branded phones, you would think they...
Oh yes. I spent some time on the phone and in online chat with T-Mobile reps. Their 1st excuse was that wi-fi calling was not available in prepaid...
It's an unlocked phone. Not purchased from T-Mobile.
I just bought a phone capable of WiFi calling - Xperia XZ2 Compact. I have the $40 Simply Prepaid plan. I tried WiFi calling using the Digits app...
