Lex and his wife have identical Samsung international phones. But when they travel to Richmond, VA, his wife's phone stops taking and receiving calls. What gives? Leo says it's because he bought an international phone. Each carrier supports different radios. So he can travel to somewhere in the US and those phones won't be supported. Leo recommends going to GSMArena, enter the model number, and it will tell what radios it supports. But his works while her phone doesn't. Leo says it's possible he doesn't have the exact same model, but very close. It could also be a configuration issue. Look and see if the phone has VOLTE enabled. It's also possible that the carrier turned off those towers, causing the problem. Or it could be a radio issue.