An excellent question. All wireless networks are not the same.
Wi-Fi is a wireless LAN technology and operates in unlicensed spectrum over fairly short ranges – up to a few tens of meters. Wide-area wireless technologies, like GSM, UMTS, CDMA, EV-DO (a CDMA technology), and WiMAX, just to name a few, operate on licensed spectrum reserved to a given carrier. These have a range of perhaps many kilometers, but, as is always the case with wireless, the further you go, the slower you go due to fading of the radio signal itself.
While Wi-Fi is subject to interference, there's a lot more spectrum available to it than is the case with cellular, and Wi-Fi spectrum is free as opposed to the big bucks – and high monthly fees – associated with wireless WANs. Tradeoffs, tradeoffs, tradeoffs. In reality, though, the two technologies will ultimately work together seamlessly – that's what fixed/mobile and mobile/mobile convergence are all about. You be hearing a lot more about these over the next few years, and eventually you won't know which wireless technology you might be using at any given moment in time.
This was first published in October 2007