www.seoatwork.com

Since Orange started offerring iphone , o2 has decided to let their users legally unlock the iphone.
All you have to do is to fill in a form on the o2 website. Within 2-3 days you will get a text message saying your phone is unlocked. Once you get the text , put your new sim in and connect to itunes and your phone is unlocked.
http://shop.o2.co.uk/update/unlockmyiphone.html
Screen shot of my unlock.