T-Mobile announced this weekend that it has appointed Michael Sievert as the company’s new chief marketing officer. Sievert began his new position today.

Sievert has 20 years of marketing experience with companies such as Clearwire, AT&T Wireless, Microsoft, IBM, and Procter & Gamble. He has twice been cited as one of the 35 most influential marketers in the U.S. by Advertising Age. Sievert was most recently the CEO of Discovery Bay Games, the maker of tablet gaming accessories such as the Atari Arcade peripheral for the iPad.

Acting CMO Andrew Sherrard will resume his duties as senor vice president of marketing for T-Mobile’s contract business. Sherrard has been serving as acting CMO since spring 2012.

“Mike is a unique creative genius, and his track record as a disruptive force in tech and telecom couldn’t be better suited to our plans to redefine wireless as America’s un-carrier,” said John Legere, president and CEO of T-Mobile USA. “This is a critical and incredibly exciting time for T-Mobile as we race forward with our network modernization and LTE launch in 2013, ramp up investments in re-launching our brand, and begin to shake up the U.S. wireless market.”

Since the proposed merger with AT&T was halted by the U.S. Justice Department last year, T-Mobile has been building out its 4G LTE network and positioning itself along with Sprint as a U.S. wireless carrier that offers truly unlimited data plans. Though T-Mobile is the fourth largest U.S. carrier in terms of subscribers, its recent merger with MetroPCS puts its subscriber number closer than ever to the third largest carrier, Sprint.

(Image courtesy T-Mobile)