An iPhone can be unlocked by the factory or by a user. When a user unlocks an iPhone the warranty is no longer valid. If you want to be able to use an iPhone on any cell phone provider’s network but retain the warranty you will need to know how to factory unlock iphone 4.
The main reason it is better to purchase an iPhone that the factory has already unlocked is that you can use it on any service provider without needing to jailbreak the phone. Although jailbreaking is not too complicated to perform, it will void the warranty on the device. However, to activate a factory unlocked iPhone to be used with your chosen carrier, you simply need to switch out the SIM cards. Take the original SIM card out and replace it with the one from your carrier. This can be very useful if you travel and need it for international calls. The CDMA iPhone is a little more difficult to activate. You will have to change the network settings on the iPhone. But it can be then be used on networks that accept this type of phone. The primary disadvantage of a factory unlocked iPhone is that it is usually a lot more expensive.