Oh come now, there has to be a signature somewhere, even if the victim did not necessarily understand what he was signing.
Don't tell me that one mobile company can just contact a rival company, say "hey, you have a Mr. SoAndSo who has signed up with us" and expect the contract to be transferred.
That can't happen, right ? So there has to be a con of some sort. You click a button, acknowledge an SMS or something and that click or acceptation is transformed into "congratulations, you've just bought a new house and signed a 50-year loan" sort of thing.
The victim has to have given some form of consent, otherwise there is no authorization to transfer.
At least, I hope so, no ?

the other goldmine is the text messages. Its amazing how easily people can subscribe to text messaging services that send things like a joke a day for a buck a day. Most of the time there is no confirmation and no clear instructions on how to remove the subscription. Since most of the time the billing department of the carrier is used to collect, it is difficult to dispute.