Depends on where you are. I know a power company engineer in the midwest that has a company supplied at&t cell phone. He gave up and got a personnel Verizon phone as it worked in his assigned sector. So when I need to talk to him I call him on his Verizon cell phone. If I don't need to talk to him I leave a message on his company at&t cell phone.
In general, Verizon has the best coverage but it has holes in service in the US also.
We will spend our old age surrounded by idiots following government rules.