How can I offer free wifi?

[chrisl]

I'm in the process of setting up my own business which will have a retail outlet. I'd like to offer free wifi but don't want to leave myself open to any legal problems in case someone does something dodgy. I have thought about some kind of sign-up process. Any suggestions for suitable hardware/software? I note that Fon have a low cost solution for small businesses but this offers just 30 mins free daily.