We have to admit we were pretty surprised last week when ATT made a pretty drastic move to preempt a rumored T-Mobile plan to pay off subscribers’ early termination fees if they switch over from rival carriers. However, it turns out that ATT and other wireless carriers might have real reason to sweat: The latest numbers from Kantar Worldpanel show that T-Mobile gained some serious momentum throughout 2013 and actually recorded more mobile sales than Sprint did for the first time over the three-month period ending November 2013. In all, T-Mobile accounted for 13.3% of all mobile phone sales in the United States over the quarter, which placed it third behind Verizon and ATT. What’s more, Kantar says that T-Mobile “also