See "Wi-Fi Hotspot Sessions to Grow to Over 11 Billion by 2014" - here and "Worldwide Wi-Fi Hotspot Usage Soars, but is Model Sustainable?" - here.
"The hotspot market continues to experience strong growth in deployed venues and usage. As with the past several years, growth in the hotspot market is largely being driven by wireless and broadband providers embracing Wi-Fi as both a competitive differentiator and enhancement to core services."
Amy Cravens, Market Analyst, In-Stat: “In the past, usage growth has largely been tied to venue growth, i.e. the more venues the more usage, and the rate of usage per venue was fairly constant. Going forward, however, usage growth will be driven by increases in connects per day at each venue. This is a result, at least in part, to a broadening base of Wi-Fi-enabled devices”