You might want to try this question on the "Computer/Internet issues" forum. Though I've no personal experience of playing with Wi-Fi outside the home, here's an interesting link about the difficulties of roaming Wi-Fi in the "real world" (wherevr that is ...):
The Register
As you'll see there's a variety of ways it works at the moment. You may be able to find areas where it's free (eg executive lounge, from a Club seat in flight), but the business model is based on charging for access. The market at present is highly fragmented so, although you can buy roaming access rights, it's not always easy to find an access point that's available to you (a bit like the early days of GSM phones).
Hope that helps!