Good news for iPhone 4, and iPhone 3GS users. Now you can permanently  unlock your iPhone 4, and iPhone 3GS by using
 IMEI unlock method.  This is a new remote unlocking method which will allow you to unlock  your iPhone 4, and iPhone 3GS on any baseband using the 
IMEI of the  iPhone. For this you don’t need to jailbreak your iPhone. As we know  Ultrasn0w can not unlock iPhone 3G, 3GS on baseband 05.14.xx, 05.15.xx  and 05.16.xx but using IMEI unlock method
 you can unlock your iPhone  3G, 3GS on baseband 05.14.xx, 05.15.xx and 05.16.xx.
Now We have Four  Methods To Unlock Our iPhone
Method 1: Ultrasn0w
This is the most public method available for iPhone unlocking. As you  know 
Ultrasnow working is based on  iPhone basebands (
01.59.00  / 04.26.08 / 05.11.07 / 05.12.01 / 05.13.04 / 06.15.00) these  basebands can be unlocked using 
Ultrasnow. It is to remind you  that a jailbroken iPhone is required to install 
Ultrasnow on your  device.
Unfortunately Ultrasn0w doesn’t support the latest basebands (
02.10.04  / 03.10.01 / 04.10.01 / 05.14.02 / 05.15.04) and we still waiting  for the 
lastest  Ultrasnow by the Dev-team that will unlock all above mentioned  basebands.
Method 2: Gevey  SIM
In this method you have to use a special SIM and call at 112 emergency  number to get your phone activated, which might 
be illegal  in some countries. Moreover it does not support all firmwares  and basebands So it only unlock iPhone 4 running iOS 4.1 and 4.2.1  basebands 2.10.04 and 3.10.01. You will found troubles on following some  steps on every reboot to get the signals of unsupported carrier. In  contrast to 
Ultrasnow, you also have to pay few bucks to get it.
Method 3: Rebel  Micro Sim Card.
Rebel Micro Sim Card may be similar to Gevey SIM, Rebel Sim can unlocks iPhone 4  basebands 1.59.00 / 03:10.01 / 02.10.04 / 04.10.01 running iOS  4, iOS 4.1, 4.2, 4.2.1, 4.3 & 4.3.1. The Rebel Micro Sim  developer may be trying to solve the Gevey sim  Problems
Rebel Micro Is like an Untethered Jailbreak means if you reboot your  iPhone so you don’t have to do the procedure again and again. The  signals will come up automatically.
It costs GBP 40 for Rebel Pro and GBP 30 for Rebel Lite. We don't know  more about the that sim or the sim problems cause it sill new sim
Method 4: IMEI  unlock
@MuscleNerd  the well  -established online unlockers for other cellphone brands are suddenly  today selling iphone unlocks..obviously something opened up
@ Chronic iPhone is being repaired now so can’t test, but I  know @CutYourSim is legit thru past dealings. I’m  positive his unlock offerings are legit.
Notes: that 
IMEI unlock  method is an official iPhone unlock so it does not affect your  warranty status.
price of IMEI unlock method:  is  almost thrice as compared to 
GEVEY SIM ranging between $150 to  $200 USD.
If you don’t want to pay money for unlock then you can wait for the free  
Ultrasn0w unlock.