San Francisco International Airport (SFO) will stop charging for Wi-Fi: On 1 Sept 2010, SFO will offer free Wi-Fi as T-Mobile's contract expires. It's increasingly common for airports of all sizes to go free; Seattle-Tacoma dropped charges in January, for instance, and Atlanta is considering the move.
The Bay Area is a unique case, in that San Jose and Oakland had already chosen to remove fees; those two relatively small airports that have non-stop flights to long-haul destinations can provide Wi-Fi at likely a fraction the cost of the massive and sprawling SFO. But SFO may want to compete effectively against its two alternatives. Sacramento clearly chose to offer free Wi-Fi years ago to attract some travelers inland north instead of south to the bay.
I spoke to Boingo Wireless recently about the trend of free airport Wi-Fi, and Christian Gunning explained that while there's ongoing interest in operating Internet service by airports without charging passengers, the fiscal realities of a down economy and the costs of operations put this out of reach of most authorities.
Coupled with that, Gunning noted, free Wi-Fi brings with it substantially higher levels of usage that mean either increased spending for the necessary backhaul or disappointment in the quality of congested service.