As of the end of March, the carrier had about 20.1 million contract subscribers and 6 million pay-as-you-go users, and those close to the subject are saying that the numbers are on the rise, which would be a big change for T-Mobile. The carrier had been consistently losing subscribers since mid-2010.
The T-Mobile press event is just getting started, so we could hear more. But, if the news is true, this would put T-Mobile well ahead of plans, which didn't expect subscriber growth for another 6 months or so. The official quarterly report is planned for August 8th.