Philipp Humm, CEO of T-Mobile USA, has resigned. Jim Alling, Chief Operating Officer of T-Mobile USA, will take over the duties of CEO on an interim basis.

In a blog on the company's website, Alling posted a letter he sent to T-Mobile employees which stressed that the carrier would continue with its "challenger strategy" and network modernization efforts as it searches for a new CEO.

"While we may be in a high-tech industry, I firmly believe T-Mobile is a people-based business," Alling wrote. "I have the utmost confidence in everyone at T-Mobile to not only deliver for our customers, but to support each other as we continue to build momentum around our strategy."

Humm's resignation comes in the wake of news this week about a spectrum swapping deal between T-Mobile and Verizon Wireless. The swap gives T-Mobile spectrum covering 60 million people in major markets, and Verizon will gain spectrum covering 22 million people, plus an undisclosed cash payment from T-Mobile.

As a result of that deal, T-mobile withdrew its petition of the FCC to stop Verizon's proposed purchase of AWS spectrum from four different cable companies.

T-mobile is currently in the middle of a $4 billion 4G network evolution plan, that includes and the modernization of its existing networks and deployment of LTE in 2013.