I bought a Archos 8o G9 tablet a month or so back, it's a brilliant piece of kit. I use mine indoors via my BT Home Hub, I can also use it outdoors in most places via the BT WiFi Fon network for free as Barrie mentions, and I also bought the correct Archos 3G stick for it (on the 3 network) for use in locations where there's no connection to the BT network. I find that the 3 network gives me super connection wherever I go.
The 3G stick costs me £10 a month to top up, I don't have to top it up if I don't want or need to, and that £10 gives me 1gB of data to play with, which takes some using.
With what I have I find I can connect to the 'net more or less anywhere I go one way or another...if there's no BT WiFi connection available, then there always seems to be a 3 connection available. Or vice versa...