Generally speaking WiFi is local and Wireless is a Phone Plan.
Phone Plans are expensive and WiFi is not so you connect to your Local WiFi and it costs you nothing more than the cost of powering the WiFi Device and your ISP connection. If you want to use the 3/4G Phone Network that is expensive and requires a Data Plan from one of the Telco's.
Though there are also Security Issues if you use a Public WiFi Hot Spot as it is possible that someone else can read your Device and Data Transfer.
WiFi relies on the 802.11 Spectrum and the Phone 3/4G System is a different kettle of fish.
Keep Up with TechRepublic