T-Mobile USA chief executive Philipp Humm resigned Wednesday, six months after a planned merger of the telecom group with AT&T fell apart.
T-Mobile's parent, German-based Deutsche Telekom, said chief operating officer Jim Alling will take over the duties of CEO on an interim basis while a search is underway.
A T-Mobile statement said Humm "is going to pursue a career outside of Deutsche Telekom so as to reunite with his family, which stayed back in Europe."
Humm joined Deutsche Telekom in 2005, and was initially responsible for the company's mobile business in Germany. He moved to T-Mobile USA in 2010 and became CEO in November of that year.
"Philipp Humm has given the company some important initiatives over the past years," said Deutsche Telekom chief Rene Obermann.
"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."
AT&T in December abandoned a $39 billion effort to buy T-Mobile after US authorities moved to block the deal as anti-competitive.