T-Mobile finally has a new chief executive: this morning parent company Deutsche Telekom announced that it has named John Legere, former CEO of the IP services company Global Crossing, as T-Mobile’s new CEO.

Following the failed AT&T/T-Mobile merger, former CEO Philipp Humm jumped ship to head Vodafone Europe. Since then, T-Mobile chief operating officer Jim Alling has served as the company’s CEO. With Legere’s announcement, Alling will step back to his COO role.

Legere also served as a Dell senior vice president, where he headed up Europe, Middle east, Africa, and Asia-Pacific operations. He also served as president of AT&T Asia, as well as other senior roles within that company, during the ’80s.

At this point, T-Mobile needs whatever help it can get. The fourth-place U.S. carrier has been steadily losing subscribers  over the past few years, primarily because it still doesn’t have the iPhone. After the AT&T merger fell through, T-Mobile announced a $4 billion “challenger strategy” to deploy LTE 4G by 2013. But by the time that network lights up, the company will be well behind Verizon and AT&T’s more mature LTE networks.

T-Mobile won’t be able to officially offer the iPhone until it has LTE up and running, although even that is far from a sure thing. For now, the carrier is trying to coax unlocked iPhone owners onto its 3G and 4G HSPA+ network (although its faster network isn’t yet available to iPhone owners in many locations).