Grandfather Schmanfather. I bet ATT will drop Unlimited completely by the time iPhone 5 rolls out.
doubtful, since people on the unlimited plan will be able to cancel their contracts without paying the ETF if AT&T force them to drop the unlimited, since it will be a change in service.
They more than likely will not grandfather in unlimited to iPhone 5 but if you keep an iPhone 4 you should get unlimited for 2 years from july 2010