There are a handful of mobile virtual network operators (MVNOs) that operate over AT&T’s network. In general, these MVNOs offer coverage profiles similar to the coverage profile AT&T offers to its own subscribers. In many cases, wireless service offered by MVNOs will be much cheaper than wireless service offered directly by AT&T.

Subscribers using MVNOs that operate over AT&T’s network are likely to have lower priority than AT&T’s own subscribers. Accordingly, MVNO subscribers may experience especially slow data speeds during periods of network congestion.

List of AT&T MVNOs

CarrierEstimated subscribersRecommended?Notes:
Consumer Cellular3,000,000
Red Pocket Mobile200,000
H20 Wireless1,000,000
AT&T Prepaid7,000,000
NET10 Wireless*3,000,000NET10 is part of TracFone
TracFoneAdditional subscribers may use other carriers that are part of TracFone. An América Móvil (TracFone's parent company) report covering performance in the 4th quarter of 2018 indicates the company had roughly 22 million lines in the U.S.
Unreal Mobile100,000
Straight Talk*9,000,000Straight Talk is a TracFone brand.
Clearway Wireless*Clearway is a TracFone brand. I believe Clearway works with all of the Big Four networks, but I'm not confident.
Beast Mobile10,000
Pure TalkUSA