How much would it cost to unlock an iPhone for that's o2 to orange?

I have an iPhone 4 handset that;s locked to o2, but I need it on orange, how much would this cost?

Added (1). In £'s

PAY MONTHLY = FREE
PAYG = £15

Pay Monthly customers

If you're a Pay Monthly customer, then you can unlock your iPhone* at anytime for free. This doesn't affect your contract though - you'll still need to see out the rest of it. This policy may vary according to the handset you have purchased.

To unlock your phone, just fill out this unlocking form and we'll do the rest.

Please make sure you enter the mobile number that you purchased the phone with, as this will avoid any charges being incurred.

Once we've got your form, it'll then take up to 10 days for us to get it unlocked for you. Once it's unlocked, we'll text you to let you know. You can then put a non-O2 Sim into the iPhone and connect it to iTunes.iTunes will then tell you the phone is unlocked.

Pay & Go customers

Yes, you can unlock your iPhone*. You'll need to pay a £15.00 one off fee and we'll take this from the credit on your phone. This policy may vary according to the handset you have purchased.

If you're unlocking your phone less than 12 months after you bought it, we'll take off the free Web Bolt On (that we added for the first 12 months). If you want to keep the Bolt On (it costs £10 a month), just choose the option when you're filling out the unlocking form. Find out more about the Web Bolt here

Once we've got your form, it'll then take up to 10 working days for us to get it unlocked for you. Once it's unlocked, we'll text you to let you know. You can then put a non-O2 Sim into the iPhone and connect it to iTunes.iTunes will then tell you the phone is unlocked.