Factory permanent unlock by IMEI
This unlock method unlocks permanently your iPhone allowing to be used with any sim card wordwide .This unlock is permanent, so will be able to update your software ( iOS firmware) without any problem. The unlock does not do any changes to your phone so will not affect your warranty or be able to cause any software issue to your iPhone. Also is very simple ,as you only have to send the IMEI number, and the actual unlock is done on the apple server ,where your IMEI is change to be recognized as unlocked .Once that change is done on the servers, you will receive an email confirming the unlock was successful and all you have to do is insert a sim from another network and connect to iTunes .The iPhone will be activated and the unlock will be completed.
Software unlock after jailbreaking your phone
This method involves jailbreaking your iPhone first, then the unlock is done trought a program from Cydia called ultrasn0w.If you are new to jailbreak can read more about what it is and how is done in this article here. The main part is the jailbreak which involves connecting the phone to the pc by usb, and doing some modifications to your phone software with the help of some programs you need to download on your pc. This unlock method is not permanent and as soon you update or restore ,will lose the jailbreak, and consequently the unlock to.
Advantages and disadvantaged of the 2 methods
-the software unlock is basically free, you can do it by yourself by following different tutorials online.The main problem is that is don’t know exactly what you are doing can damage your iPhone. Can also pay someone to do it online for you, for example at onlineunlocks.com, the online software unlock is 12.99$
-the price for the permanent unlock depends on the network the iPhone was locked to.For some networks like AT&T USA the prices are very good, half of the amount would pay for an online software unlock, but for others can be even more then 100$
-Of course the permanent IMEI unlock is a lot more easy to do, since you only have to submit the IMEI , then connect phone to pc to activate. The software unlock is more complicated and if you decide to do it by yourself have to do a bit of research to be sure you do it right. If someone else is doing it for you online is just slightly more difficult then the IMEI unlock
Dependency on iPhone model and IOS firmware
-The factory unlock by IMEI for sure does not depend of the iPhone IOS firmware ,and for most networks does not matter the iPhone model. Yet, there are some networks for which only some models are supported for unlock, or where price for never iPhone 5,can be a bit bigger
-The software unlock only works for iPhone 2G,3G,3GS and 4.For iPhones 2g and 3g works for any software version since, Apple is no longer coming up with updates for this devices. For 3gs works only for the firmware for which is a jailbreak method available, last supported for jailbreak and unlock is 6.1.Also very important only iPhones 3gs older then week 34 of 2011 will be supported for unlock,that’s have digits 3-5 of its Serial Number lower then 134. iPhone 4 can only be unlocked with the software method is if has the modem firmware 01.59.00,can find that in Settings/Genneral/About.
-The IMEI unlock for sure will not affect your iPhone at all. The software unlock is safe as long as you know what you are doing and perform everything correctly. In worst case can end up even with a bricked iPhone if you do something wrong
-The IMEI unlock will not affect the warranty in any case, because no modifications are done to the phone. Even the software unlock and jailbreak damages the warranty, because you make changes to the phone software, that can be fixed by an update or restore to stock firmware.
-The IMEI unlock duration also depends of the network the iPhone is locked to ,so it can take from a few hours to more then 15 days. The software unlock basically could be done in less then 30 min. If you are new to this and considering the time needed for reading and understanding the process, the fact that may not work from first try an take more then a day of playing with this on your pc. But if you like this kind of stuff it can be fun, at least for me it was when I did that first time.
What do I recommend?
Normally is better to use the factory unlock, because is permanent and will allow you to update without problem .For some networks the price for the unlock unfortunately is so high, that is not worth it. So specially for older iPhone models for which the permanent unlock is very expensive, the software unlock is a good solution.