(Reuters) - SoftBank Corp 9984.T is in talks with Deutsche Telekom AG DTEGn.DE over a possible deal for T-Mobile US Inc TMUS.N, as the Japanese company looks for alternatives to enter the U.S. wireless market if its deal with Sprint Nextel Corp S.N falls apart, three sources familiar with the matter said on Friday. SoftBank and Deutsche Telekom were in talks last year about a deal for T-Mobile USA