I don't know about bringing it down though, as much $$$ as they have milked from iphone customers already, they are pretty much set up to do whatever they want from here on out.
Well, if they decide to enter into any investments (upgrading infrastructure, etc.) relying on money they will make in the future (from the iPhone crowd) and don't make that money (because people jump ship), this could lead to big trouble. However, I'm sure they are not stupid enough to believe that all these new subscribers Apple has brought to them are permanent.