Method 1
Ultrasn0w Unlock: This is a software based unlock for iPhone 4 which requires jailbreaking your device and is available on cydia.
see an example on how to JAILBREAK here.
you can jailbreak using Jailbreak me if you are on version 4.3.3, or limera1n, or green poison or snow breeze or pwnagetool.
Merits
free to download and install
Demerits
requires jaibreaking
only available upto iphone4 on baseband 01.59.00
unlock lost during update.
Method 2
this is a hardware unlock procedure in which the Gevey SIM interposer is used to unlock the phone
Merits
Requires no jail breaking
easy to unlock
available on eBay and amazon
can unlock all base bands and firmwares
Demerits
expensive
fake sims are always available
Method 3
IMEI unlock
in this method the provider will take your IMEI number which is unique to every mobile devie and then the same is put into Apple’s White list. so when u sync to your iTunes next time it gets permanentally unlocked
Merits
official permanenet unlcok
unlock is not lost and works exactly like factory unlock
demerits
very expensive.
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