O2 offer unlocking for their iPhone customers, unlock for iPhone 4 appears to be working now as well!
link for unlock request form:https://www.o2.co.uk/apps/help/help?qid=1&q1=2&route=unlocking&case=Handset%20Unlocking%20Form
Even though the unlockmyiphone page on o2's website says they are not unlocking the iphone 4 yet, I just filled out the unlock request form a couple days ago anyway.
I just putting down "iPhone" for phone model, this morning I got a text from O2 saying that my iphone is unlocked. Tested by sticking an orange sim card into the phone and connecting to itunes, and successfully got the message in itunes that my iphone is now unlocked!
I had tried this a few times since the iphone 4 launch and each time got a text from O2 saying they cannot unlock my iphone. Even though I had confirmed with an online chat to O2 that they would be unlocking the iPhone in the near future.
The unlock my iphone webpage still says: "we won't unlock iPhone 4 until after the launch period. Please check back here for the latest information on unlocking iPhone 4"
This is the legitimate way for O2 customers to get their iphones unlocked.
Now to enjoy OS 4.2 on my unlocked iPhone 4!!
it appears from the comments that O2 are officially going to start unlocking iPhone 4 on monday! thanks to phoenix123 and henryftw
Also those on payg who have friends on contract with O2 (doesn't even have to be iphone contract as there is no difference now) just ask them to fill it in and you should be able to get it unlocked for free too.