Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
If anybody has an answer to the question if you drop to a $15 plan, from a $30 plan, can you go back to a $30 plan at your leisure, this would be very good info.
Once you stop/switch away from the grandfathered $30 unlimited plan, you cannot switch back to it.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.