Got this from T-Mobile a few minutes ago:

Please be advised you may experience problems with the following:
Ticket Number: T002125707
Service(s): BlackBerry
Fault Description: Customers in all markets may experience intermittent issues when sending and receiving e-mail from Black Berry devices. E-mail may not be delivered to their e-mail accounts and they may get a red X when attempting to send e-mail.
Market(s): All
Geographic Location(s): All.
The Estimated Time to Resolution is: 2 Hours.