T-Mobile CEO John Legere takes to Twitter following the announcement of Sprint's new CEO. Reuters

Welcome to the mobile wars, Marcelo Claure! Sprint Corp.'s (NYSE:S) new president and CEO found himself on the business end of a schoolboy Twitter tirade from outspoken T-Mobile US Inc. (NYSE:TMUS) CEO John Legere.

And, now that the proposed merger between Sprint and T-Mobile is officially off, the gloves came off, too.

A slew of other tweets followed, in which Legere, 55, referenced Sprint's "framily fued" and how Claure, 43, will have to exercise some "framily therapy," a play on the mobile network's service share plan that customers can utilize between family and friends.

"Pro-tip for @marceloclaure, tell people how to pronounce your name now... #leegair!?" Legere tweeted at Claure. Legere, whose last name is pronounced as "ledger," quipped that it's often mispronounced as "leegair."

Claure, who's the founder and CEO of Brightstar Corp., a Miami-based wireless distributor that's already a subsidiary of Sprint parent company Softbank, has been a member of Sprint’s board since January. Legere's tweets about "framily problems" allude to the fact that Sprint selected someone from inside the company as its new CEO. Claure will succeed Dan Hesse, who had served as Sprint CEO since 2007, on Monday.