Unlock your apple iphone 4 and use any other carriers sim card
To unlock your apple iphone to use any sim card, you need to get the unlocked confirmation from apple by using any unlock code service provider.After getting the unlock confirmation you need to use i-tune to unlock it
here is the direct link of service provider to get the unlocked confirmation
How to unlock iPhone Factory Unlock iPhone
After getting the unlock confirmation you need to use i-tune to unlock it as below:-
How to Unlock the Apple iPhone 6 after getting the confirmation as Unlocked -
-Install the last version of iTunes on your computer.
-Make sure your iPhone 6 is updated with the lastest version of iOS.
-Switch ON your iPhone 6 with a SIM Card from a non-compatible network.
-Connect your iPhone 6 to your computer using the Original USB Cable.
-Launch iTunes andwait until iTunes detect your iPhone 6.
-Now disconnect your iPhone 6sand reconnect it after 10 seconds.
-Your iPhone 6 is now Unlocked!
Note:-In the unlikely event that your iPhone 6s is not unlocked, please restore your device following the official guideline from Apple - https://support.apple.com/en-us/HT201252