AT&T is probably going to be pushed to do so by the continued existence of T-Mobile. We're lucky that deal didn't get through, or you can be sure you wouldn't be able to have SIM-only plans.

My guess is Verizon will block this point-blank, and refuse to activate the phones. It'll take a change in the legal landscape to compel them to do so. They already have Android phones coming out of their ears, plus the iPhone, so they have no need to play nice with Google, particularly if Google isn't willing to use Motorola to play hardball.