Permanent unlocking for iPhone 3GS
This servise is used for network unlocking all iPhone models.
In order to unlock an Apple device you need to provide the IMEI number(phone serial number), which can be found by dialing *#06#, or by checking in the phone settings.
The next important thing is to provide the correct network for unlocking.
You always remove the blockade from the network in which the phone is working, not the one that you will be using in the future.
If you don't know the network you can use this service to help you check.
The last thing is to check if the IMEI number is blacklisted.
Blacklist means that the IMEI number has been reported as stolen, lost, damaged or the bills where not paid for the contract.
When this happens the signal of a blacklisted device is blocked, and it won't work in the country it is blacklisted.
It also means that there is a different service required to remove the network blockade.
If you don't know if you device is blacklisted you can use this service: black list checker