There are various methods of unlocking a carrier locked iPhone. You must unlock your iPhone device first so that you can use any carrier GSM network on it all around the world without any restrictions. All carrier locked iPhone models can be unlocked easily.
Locked iPhones can be a real headache for you while traveling abroad. If an iPhone is GSM carrier locked then it doesn't give you privilege to use GSM networks outside your country. For this reason, you have had to unlock your device so you can use any network worldwide on it.