Guess T-Mobile USA’s chief executive Philipp Humm received an offer he couldn’t refuse. Today he announced it was his last day with T-mobile to join a rival firm. Details about his resignation after the jump.

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T-Mobile USA’s chief executive Philipp Humm suddenly resigned on Wednesday, the company said.

Chief operating officer Jim Alling will take on the role as interim chief executive until the position can be filled.

René Obermann, the chief executive of T-Mobile USA’s parent company, Deutsche Telekom, said in a statement:

“Philipp Humm has given the company some important initiatives over the past years: Under his leadership the cost situation at T-Mobile USA has vastly improved and he led the company during a difficult phase regarding the planned merger with AT&T.”

But he added what appears to be the crucial line regarding his successor:

“Now we need somebody who can convert initiatives into market-successes.”

German born Humm joined T-Mobile USA two years ago while his family stayed behind in Europe. He first joined Deutsche Telekom in 2005, taking over as chief executive within six months.

With all eyes currently on Google I/O, the timing of this news is interesting.

Alling sent an immediate email to all T-Mobile USA employees, stating: “Philipp Humm has decided to leave the business”, suggesting he walked out on his own terms.

However, a leaked memo from Obermann said — again to all T-Mobile USA employees — at 9:15 a.m. on Wednesday morning: “Philipp informed me a few days ago that he will be joining a competitor of Deutsche Telekom.”

Update (14:10 ET): A Deutsche Telekom spokesperson confirmed that Humm would join one of the company’s competitors “in the future.” As Humm plans to return to his family in Europe, the likely guess is that he will join a European firm.

“In April, Philipp informed me that he intended to end his contract at the end of September,” the note added. “This search is progressing well. I have spoken to a number of promising candidates.”

No wonder Obermann sounded like he was twisting in the knife towards the end of his public statement.

Humm joined the company at a difficult time, overseeing the acquisition of AT&T for $39 billion — a task he was charged with overseeing — which eventually fell through.

The merger collapsed after it failed to gain support from the U.S. Federal Communications Commission — a step necessary for the deal to go through. The U.S. Justice Dept. eventually sued to block the merger on the grounds that it would “substantially lessen competition”.

Since then, Deutsche Telekom had been trying to sell off the company, but noted to shareholders earlier this year that a complete sale of the U.S. network is “unlikely.”

ZDNET