This is information gleaned from an old article in USA Today. For more updated information try this Wi Fi in Airports website: http://www.wififreespot.com/airport.html
In 2005, and I think still, only a small number of companies control most airport Wi-Fi. Here are some:
Wayport. San Jose and Austin. Limited coverage in Oakland, Calif. Airports: AUS, BUF, DFW, OAK, SJC.
Cingular. Denver, Seattle, and Philadelphia. Airports: DEN, PHL, RDU, SEA.
ICOA/WiSE are now merged
ICOA: GEG, BTR SMF, MHT, SAV, FYI, GRK, CHS, ORF, BQK, AZO.
WiSE: ELP, LGA, BWI, CHA, OMA, PBI, ANC, SAN, JFK, IAH, BUF.
SBC. PSP, CLE, BUR, LIT, EVV.
A private contractor for cell and Wi-Fi installations. BNA, DTW, EWR, JFK, MSP, YOW.
T-Mobile. Another veteran hotspot provider with over 5,700 coffeeshop, bookstores, and retail locations, they also offer airport-wide coverage. Airports: SFO, BUR, BWI, GSO, PVD, FSD, TYS, AUS, DFW, DAL, ORF.
Sprint PCS. KCI, SLC, HOU, MEM, MKE, SDF, OAK.
Opti-Fi. Full coverage: YEG, DSM, PHF, ELP, SBN, MOB, MLB, TVC, ALB, YQQ, YHM, YQT, JNU, JAC, ASE, YQG, TOL.
AirTran only: ATL, BWI, DAY, FNT, MDW, MEM, MIA, MKE, ROC, JAX.
Airport’s own WIFI networks: These airports rolled their own WiFi, and deserve alot of props for doing it! OWD, FRG, BOS, PDX, LAS, MFR, YUM, ISP, ASE, SAT.
This list is old and NOT INCLUSIVE! Many Airports are adding this great service – be sure to send them a note thanking them if they provide free WiFi!