I had a Sony Ericsson K800i back in the day on 3 and I unlocked it before selling it?
I was trying to do it via the internet without forking out. 3 phones are notoriously difficult to unlock (apparently) and the model I have doesn't appear on the sites as one of the ones easy to unlock.
I could pay 15 quid to 3 via my mate, but hate that company with such a passion I'd sooner buy a new one rather than give them a penny.