Here's what consumers have asked with answers from IPhoneUnlock.Zone staff and previous consumers.
Hello Alison. I am afraid that there are no O2 UK IMEI Unblacklist services available for the time being. The best way to remove it, would be to either contact the previous owner of that device and ask him to remove it OR if you have the original purchase receipt, call O2 UK network, inform them that you are the owner and ask them to remove it.
Hello Silent. If your iPhone is Blacklisted and Locked by AT&T USA network, first you need to remove the Blacklist status and THEN unlock it. Those are two individual services and in order for the unlock to be successful, the Blacklist removal should first be a success. I suggest our iPhone IMEI Unlock Check service, which will identify the problems of your iPhone and check if after the Unblacklist service, an unlock will be possible (It depends on the Financial and Contract status of your iPhone).