If you would like to unlock your iphone from o2 to use with any other networks you need to go to the o2 website and fill out an unlock form which you can find here:
Monthly Contract form: unlocking form
Pay as you go form: unlocking form
This will require you to give 2 mobile numbers you contact most frequently and £15 credit on the phone that they will take of after you complete and send the form of to o2.
There are only two options, whether you consider them to be viable or not. Only the carrier can unlock your iPhone. Your carrier will not unlock your iPhone for only a short period of time. However, your carrier can provide you with special access numbers to substantially lower the cost of making and receiving phone calls while you're out of your home country.
Sorry I am currently with orange they have given me all the info to unlock it. However the only sim I can get access to on another network is on o2. I want to be able to use my phone in oz with an Aussie sim, however won't have access to my iTunes to be able to unlock it when I get there, and I also want to be back on orange when I get home, and given what they are saying I would at that point be locked into and Aussie network! I just want to know if it locks you into a New network or opens it up to move freely between sims. Hope I make a little more sense! Thanks
Haha im thinking i understand a bit better now!
I highly doubt there is anyway to unlock your iphone without your authorised itunes account on your home pc/laptop or where ever you set your iphone up.
but if you could figure a way out around that im sure when you get your carrier to facotry unlock your phone it means you are able to use any network
this is from personal experience