It was announced that T-Mobile USA Inc. Chief Executive Philipp Humm resigned Wednesday and will leave the company to reunite with his family in Europe. However, it came as a shock to many when within just 24 hours of his resignation, Humm was hired by Vodafone.

Humm will be replaced by Chief Operating Officer Jim Alling on an interim basis while a search for a successor is underway, according to the Wall Street Journal.

"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," Deutsche Telekom Chief Executive Rene Obermann said.

Vodafone Group PLC (VOD.LN) is the world's No. 1 mobile operator by revenue. It was recently unveiled that Humm will become chief executive of Vodafone's Northern & Central Europe business, overseeing operations in Germany, the U.K., the Netherlands, Turkey, Ireland, Hungary, the Czech Republic and Romania, Vodafone said Thursday.

According to the Wall Street journal, In a letter to T-Mobile USA staff released Wednesday, Deutsche Telekom Chief Executive Rene Obermann said Mr. Humm informed the company in April that he intended to leave at the end of September so he could return to his family in Europe. But Mr. Humm's exit was brought forward after he informed Mr. Obermann "a few days ago" that he would be joining a competitor of Deutsche Telekom. He didn't name the competitor at the time.

T-Mobile scored $3 billion as a breakup fee from AT&T, plus another $1 billion worth of spectrum. But the company still faces an uphill battle, as it does not have enough spectrum to deploy a competitive 4G network. So T-Mobile is expected to merge with another company, if it can figure out a deal that will receive regulatory approval.