I have used one2one in UK for data (contract service - you'd have to check if theyr PAYG service will allow data). As said above, web pages are a tad slow (though I've used it for them when I got to the hotel one evening and realised I had left behind the phone number and address of the company I was visiting
) but great for email.
On the way back from the same trip, I was sending my trip report back to the guvnor, and emailing back and forth to a friend in another country - from a railway carriage en-route to Oxford - what a poseur
Only problem there was that I had to redial FreeServe when the train went briefly "out of coverage" a few times
(but now I find it easier to use a cable from laptop to phone, instead of I/R most of the time)