Factory unlock iPhone 5 contract?

So I got a pay monthly contract iPhone 5 on O2. The phone contract will expire in a few Month and I was thinking if its possible to factory unlock it before the contract its expired, and if I can unlock it before the contract expires will O2 blacklist my iPhone 5?

By my understanding if the phone is from a company an you try to flash it to another company this can only be done once, if O2 sold you the phone, with the contract then they should not blacklist you unless you bought the phone from someone else and flashed it to O2, unlocking is mainly if your switching services it's a 50/50 chance they will black list you

I used www.unlock-4.me to unlock my iPhone couple months back, it is free but if you donate you get your unlock instant. I didn't have a problem, you are even able to update your phone unlike if you were to jailbreak it. I'd definitely go check them out. You won't get black listed using unlock-4.me it is 100% safe.