I don't believe they have any plans. That's why I'm floating the idea. There are things that are easy to do which end up being hard because the underlying systems are mucked up. Sometimes something that is just an accounting change can still be a nightmare if the accounting wasn't designed flexibly. So I make no bets about how long they would have to do it. That there is nothing inherently hard should not be a matter for debate, since it's a feature people get in PBXs, which tend to be less sophisticated than full cellular switches. Cell phone companies started out be far more innovative in terms of their switching than both PBXs and 5ESS PSTN switches.

Of course, the only things that actually could be hard to do are not actually necessary, they just would be implemented to discourage people from cheating on the system and having two phones used by two people. Charging 10 cents/minute for calls on the supplemental phone would solve most of those problems, since people wanting a 2nd fully functional phone for 10 cents/minute can already buy that in the prepaid market from T-mobile.