Best zero outlay pay monthly deal I could find on the S2. Contract is with T-Mobile through affordablemobiles.co.uk. Topcashback tracks at £60.60 on this deal if you go via there first. Also first 2 months half price via redemption.
As of 01/07/2011, those signing up for this get their truly unlimited deal included:http://t-mobilenewscentre.co.uk/truly-unlimited-internet-on-your-phone/
Literally unlimited (no cap) data allowance for the phone. Only stipulation is not to be used for tethering apparently.