COMEBACK: Unlimited data plans are returning as smaller wireless companies try to compete with AT&T and Verizon.

THE ANNOUNCEMENTS: T-Mobile USA will start selling an unlimited-data plan again on Sept. 5, after stopping sales of such plans early last year. MetroPCS cut the price of its unlimited-data plan as a promotion for a limited time.

THE TIMING: The moves by T-Mobile and MetroPCS, neither of which sells the iPhone, come as their three larger rivals are thought to be gearing up to begin selling the iPhone 5 in a month or so.