Apple made their iPhone firmware update available to the public before making it available via iTunes. The file itself weighs in at 160MB and can be downloaded here: iPhone Firmware 1.1.2
The only problem has been the lack of information on how to install the giant file. Although many people have linked to the file, a lot people have struggled to figure out how to install it. Fortunately, it’s an easy process.
Step 1: In iTunes, on the iPhone screen, Option+Click the Restore button (for Windows users it’s Shift+Click).
That’s it! Just one step, then follow the instructions.