T-Mobile's all-time number one seller is the Samsung Galaxy S III
It is not as though T-Mobile hasn't had some awesome phones in the past. Of course, there was the current champ's predecessor, the Samsung Galaxy S II which at one time was called the "Best Android phone ever," a title it held until the sequel was launched. And in the era when a 3.5 inch screen was considered "generous", the HTC HD2 was a T-Mobile exclusive in the states with 4.3 inches of Windows Mobile goodness.
easy as changing breakfast cereals, those who want an Apple iPhone badly enough can leave T-Mobile for a carrier that offers it.
By the time the Samsung Galaxy S III is retired to the dreaded EOL list, it will continue to set a new T-Mobile record with each sale. The only real question is whether the Samsung Galaxy S IV will surpass whatever final tally the Galaxy S III earns.
source: T-Mobile via RedmondPie