well what i know you can unlock iphone 3gs with iPhone OS 3.0 Jailbreak.This is the Easiest unlock available today! Super fast unlock for all versions, fully iPhone optimized.enables you to activate any iPhone on any network, any carrier, any SIM card. No need to provide any information to AT&T, This is not a technical hardware unlock, No need to soldering/opening your iPhone You can restore your iPhone to original state, You can use it on as many iPhones you want, works with any iPhone, any Provider, any Simcard

I think, all mobile phones can get unlocked. You only have to find someone will to give you the right program or is doing the unlock job for you.

UNLOCK YOUR IPHONE 3g-s * The unlock about to be released works exclusively with baseband 02.28.00. This baseband is provided by the latest firmware update (2.2) from Apple. You’ll need to upgrade to this release using iTunes and then use QuickPwn to activate etc. There are plenty of tutorials about this on iclarified, bigboss, and other established tutorial sites. Because it works on 02.28.00, it is available to everyone on the planet. This means we don’t need to unnecessarily expose holes in earlier basebands, which is an important concern.
* The application is a small daemon that is launched on boot. It injects the payload at boot and also whenever there is a baseband reset. You won’t notice anything about it other than that your third-party sim now works. It’s a small program and unobtrusive. There is no GUI (this is by design).
* You can add the application using the sources outlined below There are Cydia and Installer sources available, so use whichever you are comfortable using.
* yellowsn0w is completely removable through Cydia, the command line, and iTunes.
RELEASE INFO
* Cydia source: http://apt9.yellowsn0w.com/
* Installer repo: http://i.yellowsn0w.com/