In other words, to my question, no one really knows how they "force" you to return your phone, correct? As, from dave006's version, nothing special happens -- if you terminate before the end of the first month, you just get the ETF, you lose your initial payment and your activation fee, and you keep the phone. Your theory that they invoice you for the $599-699 is interesting, but no one seems to have any evidence of it actually having happened. It also sounds somewhat suspect, considering that you would be charged significantly more than if you had kept the contract active for a month, without being provided any additional services, although perhaps they can get away with it if that's what the contract stipulates.
So has anyone actually gone through this process (trying to terminate before the conclusion of the first month and refusing to return the phone), and if so, what actually happened?