Deutsche Telekom merged its T-Mobile USA unit with prepaid specialist MetroPCS in 2013, creating T-Mobile US. Following the merger, the firm provided nationwide service in major markets but spottier coverage elsewhere. T-Mobile has spent aggressively on low-frequency spectrum, well suited to broad coverage, and has substantially expanded its geographic footprint. This expansion, coupled with aggressive marketing and innovative offerings, has produced rapid customer growth. The firm serves 37 million postpaid and 21 million prepaid phone customers, equal to about 19% of the retail wireless market, and about 16 million wholesale customers through offerings like America Movil's TracFone. T-Mobile is the third- largest carrier in the U.S., trailing AT&T and Verizon.