If you spend any time watching television ads, it may seem like Verizon, AT&T and Sprint are the only three cell-phone carriers in the country. However, there are a handful of smaller companies that are trying to elbow their way into the big time, and T-Mobile made strides in that direction this year with its acquisition of MetroPCS. The merger gives the combined firm a user base of 42.5 million, just shy of third-place Sprint’s 56.4 million users. Along with the expanded user base, T-Mobile executives hope that cost savings from the merger will give the firm the needed firepower to compete with larger carriers as those firms invest in faster, more expansive coverage.