Have a look here.
http://www.zdnet.co.uk/specials/wifimap/
This should tell you everything you need to know, inc maps of wi-fi locations and prices.
You're correct in your assumption about accessing the internet, without having a landline, provided it's done from a hotspot.
(note to the mod's).
zdnet allow their info to be linked.
"Links:
You may link from another site to ZDNet UK online content including reviews, articles, features, video and audio clips."