This will update your Baseband so that you have the latest modem on your iPhone. It means you can use Google Locate without the need to run any additional 3rd party apps. The best part is you keep all your apps, customizations and jailbreak and after following the second tutorial you will alo be unlocked.
FYI - make sure you read and follow every step (including putting the iPhone into Airplane mode)
AND these instructions assume and tell you that you need firmware 1.1.3. DON'T do this if you have not or are not going to upgrade to 1.1.3 first!
First of all follow this post: Upgrade Baseband Tutorial
Then follow this post: Unlock with AnySim 1.3 Tutorial
I now have 1.1.3 Firmware, 04.03.13_G Baseband, Bootloader 3.9, Unlocked and jailbroken. (which basically means Google Loacte works)