How to identify/unlock a country locked iPhone 100% Working Free

Country locked iPhone?

If the iPhone is country locked, it simply means that the iPhone will not take SIM cards from other country's carrier. This country lock is usually done by the first carrier that had the phone from the beginning.
With the case with iPhones, the country lock is processed by the apple server with the carrier's request.
To unlock the country lock, it is a must to contact the carrier that had the phone, when country unlocking is commenced, any data (photos, songs, contacts) won't be lost, since country lock is not done physically.
Unfortunately, there are cases were carriers do not allow unlocking country lock (eg. Softbank, KDDI AU from Japan).

How to identify a country locked iPhone

Insert a SIM and see if you get a signal and the carrier's name on the top left hand corner.
If you have signal and have the correct carrier's name, your phone isn't country locked.
If you get a  , or a No Service signal, try factory resetting the phone.If it still doesn't work, the phone is country locked.If the iPhone has successfully identified the SIM, the top left corner will change from
 
(in this case, the iPhone identified my Telstra SIM)
You can also check if your phone has detected the SIM or not by visiting the Settings menu.

If your Carrier Menu shows the correct SIM provider, your phone has successfully detected the SIM.

Unlocking Country lock through your provider

To unlock the country lock and use the phone, call the phone's provider / carrier and ask for country unlock. (Make sure to check if they do country unlocking)
Advise your provider with the phone's IMEI number, which is an unique 15 digits number each phone has.
Here is how you check the phone's IMEI number.

Settings - General - About - IMEI

In average, the country lock will be unlocked taking about 30 minutes ~ 24 hours max.
Make sure to unlock the phone's country lock when you are planning to use your phone overseas during your holidays or visits !