Re: Who owns the handset ?
Check your airtime agreement.
IIRC (and IANAL) this came up ~6 months ago when Orange wanted to change their call costs significantly leading to lots of subs summarily cancelling their contracts mid-term citing a major disadvantageous change in the contract.
A clause in the Orange contract was cited which states that supply of the equipment (i.e. handset) is separate to this (airtime) agreement. IOW they thought they were being clever and saying that if the handset is faulty that doesn't affect the airtime contract which remains in force, but it bit them because people were able to cancel their contract for the reason above, and keep the subsidised handset which was already theirs.
All this locking of handsets is bollocks anyway. I kinda makes some sense during the minimum contract term, but not after that regardless of any handset exclusive. I've raised with OfCrap several times that handsets should be automatically unlocked for free at the end of the fixed contract term under which they were obtained as to leave them locked after this time is uncompetitive.
As one of the commentards above said - if users were getting the best smart phone experience on O2 they wouldn't want to unlock their handset in the first place.