Apparantely they will unlock your phone for free on contract phones and £ 15 for PAYG phones from Monday.
https://www.o2.co.uk/apps/help/help?qid=1&q1=2&route=unlocking&case=Handset Unl ocking%20Form
https://www.o2.co.uk/apps/help/help?qid=1&q1=2&route=unlocking&case=Handset Unl ocking%20Form