Just read from AppleInsider that Apple has just released the latest solid 2.2.1 for the iPhone and iPod Touch, and users need iTunes 8 to update it.
This solid is suitable for:
The first iPhone, the 3G iPhone
The first iPod Touch
Second generation iPod Touch
Finally, I would like to remind you that cracked iPhone/iPod Touch, please do not update. This is only suitable for untampered iPhone/iPod Touch.
Source: AppleInsider