Both AT&T and Verizon each hold a whopping 34% of the entire mobile market in the US, dwarfing both Sprint and T-Mobile, which stand at 16% and 14% respectively.
Verizon used to be the top dog, but AT&T has been making some moves with its MVNO carriers that have helped to bring it up to speed with Big Red. In Q1 2014, AT&T managed to up their number of subscribers to 116 million, including the MVNOs, compared to Verizon's 103 million. Now this is where the numbers get a bit tricky, because if you only count AT&T's business and retail customers, then its total number of subscribers will only be 85.1 million.
Sprint has been trying to purchase T-Mobile for some time now, but has had a difficult time with convincing regulators that it is a good move. If the sale goes through, a combined T-Mobile/Sprint network would not only provide better coverage for their respective customers but give the two providers a 30% market share, making them a combined force against both AT&T and Verizon.
T-Mobile has had lots of momentum in acquiring new customers, claiming 66% of all new sign ups, which shows some promise for the nation's fourth largest carrier.