WiFi at Starbucks is offered by
T-Mobile and cost depends on what plan you want and if you are a T-Mobile subscriber.
Boingo Wireless is another provider. You can find these providers all over the country. Basically you will be able to logon to any AP the the provider offers. As far as a school, most of the time those are open hotspots, but it also depends on the policy of the school. THere are free hotspots out there, you just have to know where to look. The locally owned coffee shop I go to in the morning has a free open AP that I use to check my email before going to work. Other can be found on some sites such as this
one.