His name is David Costabile, an actor who is presently in the FX Network series, Damages. On the show he plays a crooked detective named Rick Messer, not at all as humorous a character as in the T-Mobile commercial.
If we saw the same commercial, then I think the actor you are looking for is Victor Browne. Victor Browne was in the Hallmark Channel movies Love's Unending Legacy and Love's Unfolding Dream, which were part of the Love Comes Softly series. In those movies, he plays Zach Tyler.