When they launched Overwatch 2, you couldn't play if you tried to verify your account with a prepaid phone. This was problematic since they closed Overwatch 1 servers (it's a paid, online only game) for Overwatch 2, a free to play game.

Some people found themselves that they could no longer play the Overwatch franchise after having bought the $40 original game because of this. This was later rolled back and they allowed prepaid phones. So they can definitely distinguish them.