I need a data sim for my iphone.

[philthy]

I had enough of the lousy coverage where I live, so would like to drop o2 and get a different sim. I very rarely call anyone, and hardly use texts either. Ideally, it would be some sort of data bundle, with a couple of minutes/texts chucked in.
Pay as you go for preference, as I'm not always in the UK, and don't really want to be paying for months I'm not here.
Any pointers ?