When Sprint and T-Mobile want to merge together to compete against Verizon and At&T is not just because credit is easy commodity these days, although it is definitely a nice to have for a merger of this size. If you look at the maps below, courtesy Whistleout
Look at Sprint and T-mobile’s coverage as compared to Verizon and AT&T coverage. The AT&T 4G coverage is not as thorough as the Verizon’s in pasts of the country but it is a close 2nd in the US. The investment required to erect cell sites and the time it takes to broker or buy land to install is a very time consuming endeavor that plans has to be set in motion well in advance of 2-3 years. Such daunting task of maneuvering the legal and PR process of getting permits from the local government office or a private owner in some instances is something only a very structured organization can handle. Even if you have the resources, the time taken alone makes sense to buy competition and compete with bigger network coverage. Yes, offering a cheap phone plan like Sprint and T-mobile get the customers in to the store but when that customer experience bad reception and dropped calls in more then acceptable situations, it turns them off and you would have probably done more damage having them as customers now then not have had them as your customer.
Once a phone user leaves you for bad reception and goes to another carrier to only find out how diverse the coverage area is, they are not coming back again, even when you have even better coverage then the ones they are with right now. The cost of coverage makes more sense to the consumer now that they are willing to pay what ever the competition might charge them for.