Ultrasn0w
Unlock iPhone 4S With R-SIM (iOS 5 / 5.01)
Another hardware unlock solution has appeared, the R-SIM from Each Supplier. This SIM interposer works with the iPhone 4S running iOS 5 or iOS 5.0.1 making it possible to use the device on any compatible GSM carrier network.

iPhone Dev-Team has not made recent announcements regarding updates to ultrasn0w, the software unlock solution for jailbreakers. One advantage of the R-SIM is that the product does not require a jailbroken iPhone to unlock the device.
Dev-Team Releases iPhone 3.1 Jailbreak
Here we go again. With Apple's release of iPhone OS 3.1 the iPhone Dev-Team has been busy getting jailbreak and unlock solutions ready. The first of these software packages is Pwnage Tool 3.1 for Mac OS X.
The current version is available directly from the iPhone Dev-Team and supports the first generation iPhone and the iPhone 3G. The Dev-Team is still working on software for Windows and the iPhone 3GS.
Jailbreak and Unlock iPhone Firmware 3.0.1
Apple released the iPhone OS 3.0.1 firmware update the other day to fix an SMS security flaw. This has rendered purplera1n useless, and creator Geohot has abandoned the project for now. That being said, redsn0w from the iPhone Dev-Team still works.
There's one thing to look out for when using redsn0w to jailbreak 3.0.1. After updating to the official 3.0.1 through iTunes, running redsn0w will ask for the IPSW file to use for jailbreaking. Select the 3.0 IPSW, not the 3.0.1 version you just installed. For owners of the iPhone 3GS or a newer 3G, you may not already have this file.
iPhone Dev-Team: Our Unlock Beats purplesn0w
You may be in the market for a good iPhone unlock. Everyone likes to save money roaming overseas. Some of us just can't stand our current wireless carrier and want to break free. Turns out there's more than one solution available.

Two of the top competing software packages have been released and they are very similar. Even their names, purplesn0w and ultrasn0w are so alike it can be confusing. Turns out that geohot, the developer of purplesn0w, released his source code.
How Can I Unlock My iPhone 3G?
If you're interested in using your iPhone 3G with any GSM mobile carrier the iPhone Dev-Team has the answer. Unlocking can also save a few bucks if you have AT&T and you're using your iPhone 3G outside of the US.
Using the latest release of ultrasn0w simplifies the process, but will only work with the iPhone 3G. Start out by making sure your iPhone 3G is updated to iPhone OS 3.0 and jailbroken with PwnageTool or redsn0w. T-Mobile users should disable 3G on their device.