"AT&T is doing it big time...It's an easy way to offload traffic," says Selina Cho of Ruckus, a Wi-Fi equipment company. Placing such Wi-Fi units in overburdened areas is cheaper and faster than building additional cell towers. AT&T already extended this offloading effort to individual homes, selling MicroCells that divert wireless usage to a the home's local Internet connection. Although the purpose of the MicroCell is for signal strength in low-signal areas (i.e. many areas), it also unburdens the carrier overall.
AT&T already has more than 20,000 hotspots in the US, which consumers often use for data instead of their carrier's signal. Carriers can now follow suit for their traffic (data and voice) and avoid having to build a skyline of expensive cell towers.
source: The New York Times via Textually