Another Galaxy S2 user here, recently got it, 15 a month for 1GB, unlimited texts and 300mins from Orange. That was after I mentioned to them that I'd just bought one for 15 a month (having paid 280 up front...) from a website with unlimited internet, and 300 mins/texts on T-mobile, and if they could match it I'd stay with them and give the other phone to my wife. They didn't charge me the 280 up front, and 1GB is great!
Have to say, both my wife and I are loving the phone. Upgraded from a Nokia 5800 XpressMusic which was great for listening to MP3s on my walk to work, but otherwise couldn't hold a candle to this thing.
Definitely 2 thumbs up for it here!
There is a new one just announced you may be interested by though: the Samsung Nexus Prime - that looks very good too and you might be able to get that around 30 a month possibly :)