@amerispec22y4 The reason you need a VoLTE phone to work in the USA is because there is no more 3G network there, which a non-VoLTE phone needs to make voice calls. Everyone in the States had to get a VoLTE capable and carrier approved phone by the end of 2022. Hence you find that data and texting work but voice calls don't. T-Mobile is also shutting down their 2G network as of September 1st and was spotty even before that but is worth a try as already suggested. I see AT&T doesn't list any Umidigi phones as guaranteed VoLTE capable either. Fongo is another voip app you could use and will work over cellular data and wifi.
