How to manually update iPhone 4 from ipsw file?

I followed the following steps to restore my iPhone from IPSW file:

These steps are for the following scenarios:

1. Your download in iTunes does not work!
2. You have lots of iPhones and you don’t want to download the file for all of them!
3. You just want to be a geek!

The two options bellow are self explanatory please choose one at your leisure.

“I just want it to work!” Option:

1. Updated iTunes to latest 10+ version
2. Synced and backed up iPhone in iTunes
3. Press “Download Only” when prompted to download the file and accept conditions.
4. Pause the download and close iTunes.
5. Downloaded the version of OS I wanted which was “iPhone3 4.2.1” from apple, you can get the links from here: http://iclarified.com/entry/index.php?enid=750
6. Copy the IPWS file into the iTunes/”iPhone Software Updates” folder.
7. Open iTunes it should prompt you to update your iPhone.

“Geek” Option:

1. Updated iTunes to latest 10+ version
2. Downloaded the version of OS I wanted which was “iPhone3 4.2.1” from apple, you can get the links from here: http://iclarified.com/entry/index.php?enid=750
3. Synced and backed up iPhone in iTunes
4. Shift+alt clicked on the Restore button and selected the downloaded file.
5. Waited and followed onscreen and iPhone instructions.
6. Restored a backup of iPhone settings made earlier.
7. Synced the reminded of MP3’s and apps

That’s all.

NOTES:

1. To use a manually downloaded IPSW file in iTunes you will need to hold down SHIFT+ALT and click the Restore button. On mac its Option button.
2. My Internet disconnected while it was in the process and iTunes spit the dummy and iPhone OS was mia, but I just reconnected the Internet and restarted the process, she worked as a charm after that.