The iPhone Dev Team have completed a 3G unlock for the iPhone 3G, which is expected to be released on New Year's Eve 2008. Codenamed "yellowsn0w", the unlock will work with handsets using the 2.11.07 baseband or earlier, and will require a Jailbroken iPhone 3G. The team is currently being packaged into a more user-friendly app, which will hopefully not require any especially technical skills.
They've also addressed rumors that Apple's recent 10.5.6 system update has purposefully blocked the Jailbreaking process on the smartphone. According to the Dev Team, the current belief is that this is a kernel bug rather than a specific countermeasure by Apple; they've also offered up some possible workarounds, though as with any hack you try them at your own risk:
1. Replace the following plugin kexts from within IOUSBFamily.kext with the ones from 10.5.5 and then rebuild kextcache (if you don’t understand this, then you shouldn’t attempt it!)
2. Use a USB hub in-between the DFU device and the Mac and insert/reinsert the iPhone’s USB cable.
3. Use a PwnageTool created .ipsw on Windows! Oh the irony!
We'd be interested to hear if any of these fixes issues you might be having with your iPhone after running Apple's update. Let us know in the comments.