How do I unlock my phone to change my network provider?

I am on Orange but I want to swap over to 02. I got an 02 sim today and put it in my phone but it says its locked. I called 450 (Orange) but I cannot get through to customer services because I do not have any credit. But I'm not going to top up just to call them to find out how to unlock it! How else can I unlock it?How do I unlock my phone to change my network provider?
depends on what kind of phone it is. Check eBay. Search for unlock code for your model. Prob cost you around 10 bucks to have it unlocked.How do I unlock my phone to change my network provider?
hi,

there are lots of methods avaliable to unlock your phone, the method i used to unlock my phone is through unlock codes, i procured codes from http://www.theunlockspot.com/ try if your phone is listed for unlocking