Preview at WWDC likely in June, followed by September launch.
AT&T to Throttle Unlimited Data Plan Customers Starting in October
AT&T announced today that they will be throttling high end users with unlimited data plans.
Starting October 1, smartphone customers with unlimited data plans may experience reduced speeds once their usage in a billing cycle reaches the level that puts them among the top 5 percent of heaviest data users. These customers can still use unlimited data and their speeds will be restored with the start of the next billing cycle. Before you are affected, we will provide multiple notices, including a grace period.Early AT&T iPhone customers were offered an unlimited data plan for their devices. Even after AT&T stopped offering an unlimited plan, they allowed existing customers to retain their unlimited plan through device upgrades.
This change will affect any of those users who still have an unlimited plan and are considered to be in the "top 5 percent of heaviest data users". For those users, download speeds will be reduced until the next billing month. By definition, this should affect 5% of users each month.
AT&T claims that users can still "send or receive thousands of emails, surf thousands of Web pages and watch hours of streaming video every month and not be in the top 5 percent of data users."