They don't just allow them, in some cases, they own them.(ex: at&t owns Cricket). There's a lot of price discrimination happening to try to get people to pay th

They don't just allow them, in some cases, they own them.(ex: at&t owns Cricket). There's a lot of price discrimination happening to try to get people to pay their maximum price for service. For example, I'm on Fi with my android, but my wife has an apple watch with cellular connectivity, and the only game in town was to shell out for at&t.