http://www.o2.co.uk/iphone/existingiphonecustomers
I'm thinking of getting the 16GB on my current £35/m, paying the extra for it out right. I'll be able to carry more music on it...so why not - especially with all the new apps soon to be out for it...!
Just wish they didn't want to lock us into 'yet another' 18 month contract though.