Southwest’s wifi is provided by a company called Row 44. Instead of towers, the signal is sent up from a handful of base stations to a network of geostationary satellites (the same kind used for satellite TV services). These satellites send a signal over the Ku frequency band to a much larger, more complex antenna on top of the plane.
Row 44’s service isn’t nearly as fast as what you’d get on the ground, but it’s better than Gogo’s. Row 44 doesn’t advertise specific numbers, but it’s estimated to have download speeds between 1 and 5 Mbps per user. It’s also cheaper: Southwest charges a flat fee of $8 per day.