When I first got the iPhone I always connected to Edge instead of the public wi-fi when I go for out coffee. It got really expensive cos I was downloading alot of things. So I installed 'Services' which allows me to switch off my Edge.

Then after awhile I couldn't reconnect to Edge when I was at a place with no wi-fi. So I went to Settings - General - Reset - Reset Network Settings and that resolved it all. Now I can use either Edge or wi-fi through my 'Services'. I normally switch off everything and only switch it on when I want to connect.

And to answer Obee's question if anyone can use wi-fi's at Starbucks, Dome etc, yes, I always connect at public wi-fi's and have no problem.