David Beigie, a T-Mobile spokesman, said in an e-mailed statement that the company has dispatched teams to fix the problem. The statement describes the outage as "intermittent." Beigie did not say how widespread the problem is.

Calls placed to the cell phones of several T-Mobile representatives could not be connected.

This could be the second black eye for T-Mobile, a unit of Deutsche Telekom AG, in less than a month. In October, a server failure caused customers with Sidekick-brand phones to lose much of their data.