Although this method of unlocking the i Phone is more expensive than buying a passthrough card/SIM interposer (it will run you anywhere from to 0), it is more convenient.When you IMEI unlock your i Phone it is unlocked for forever and you can update to new i OS versions, without worrying whether it will effect your unlock or not.The benefits of a software unlocking solution are of course that they are free.The obvious downfalls included limited i Phone generation and baseband support, as well as the requirement of being Jailbroken.There are many online services available for IMEI unlocking your i Phone, which you can find yourself.
If you purchase an i Phone on a contract then it is locked to that carrier until your contract runs out. When you purchase an unlocked i Phone, meaning you pay the full price for the i Phone, then it can be used with any carrier and there is no-commitments in the length you must stay with that particular carrier.
Thanks to some workarounds however, it is indeed possible to unlock a locked i Phone.
The first method to unlock an i Phone would be a hardware unlock (obviously out of scope for most people).
Unlocking the i Phone is a process where the i Phone is modified to accept the SIM card of any carrier.
Unlocking your i Phone is not the same thing as Jailbreaking your i Phone.