O2 customers can have any contract hand set they own through the network unlocked for FREE. It states this on their website and is exactly what I did when I upgraded to an Xperia Z.
Hope this helps...
Thanks for the help.
I actually got my phone unlocked for free by o2. My problem was that i bought the phone off a friend the day it came out.
Before this date i contacted o2 about buying a Z and told them that i would be travelling for a year and would need an unlocked phone. I explained that i would either be using a friends contract upgrade or buying a purple pay as you go (i wanted the purple and it was exclusive to o2). They told me that this was not a problem, and if i went for the pay as you go option i could pre order it with them and get it unlocked the day i received it for £15. If i went for the friends contract option then i could get it unlocked for free but would need to keep the contract sim in the phone for a week whilst they unlocked the phone.
I ended up getting the phone from my friend. As i didn't want to inconveniece her i installed a pay as you go o2 sim. I contacted o2 again and they told me to go top up with £20, make a phone call then call them again. They would then unlock it for the £15 from my phone credit.
When i got back to them they then told me that i couldn't unlock the phone for 12 months as that was their policy on pay as you go. They again also comfirmed that i could use the contract sim but it would have to be installed for a week.
I then spoke to a manager on the phone who read my previous online conversations with their reps and told me that they were sorry that i had been misinformed and that there was nothing they could do.
Anyway after a few phone calls and threats to take the matter further i was put through to a manager who then informed me that i had been misinformed again and that they could unlock it without the contract sim installed. So my friend called, gave in her contract details and then within a week i got the code.
So, at the end of the day i got what i wanted, minus £20 that i registered to a sim card. I am certainly not going to deal with O2 again. They misinformed me which in theory would have gained them a sale of a pay as you go xperia z. Then went against their word and would not offer anything other than a sorry even though they could see my correspondence in writing, therefore proving that the mistake was on their hands.