I've written this up for iPhone users to restore back to 8.0, feel free to share it.
Apple has pulled iOS 8.0.1 from the Developer Center and it is also no longer available via an over-the-air download. Got iOS 8.0.1 and have had the Touch ID and Cellular NO SERVICE issues? Here is how to fix that for the iPhone by reverting back to iOS 8.0.
1. Based on the model number of your iPhone, you will be able to identify which iOS firmware file you need to download. You can find model number on the iPhone’s back cover.
iPhone 4s Model Number(s): A1387 ; A1431
iOS firmware file needed:
http://appldnld.apple.com/iOS8/031-05612.20140917.FB40v/iPhone4,1_8.0_12A365_Restore.ipsw
iPhone 5 Model Number: A1428
iOS firmware file needed:
http://appldnld.apple.com/iOS8/031-05342.20140917.ZPfIL/iPhone5,1_8.0_12A365_Restore.ipsw
iPhone 5 Model Number(s): A1429 ; A1442
iOS firmware file needed:
http://appldnld.apple.com/iOS8/031-05524.20140917.0wBls/iPhone5,2_8.0_12A365_Restore.ipsw
iPhone 5c Model Number(s): A1456 ; A1532
iOS firmware file needed:
http://appldnld.apple.com/iOS8/031-05607.20140917.0Rk5V/iPhone5,3_8.0_12A365_Restore.ipsw
iPhone 5c Model Number(s): A1507 ; A1516 ; A1526 ; A1529
iOS firmware file needed:
http://appldnld.apple.com/iOS8/031-05340.20140917.F1SK7/iPhone5,4_8.0_12A365_Restore.ipsw
iPhone 5s Model Number(s): A1433 ; A1533
iOS firmware file needed:
http://appldnld.apple.com/iOS8/031-05671.20140917.dyJlj/iPhone6,1_8.0_12A365_Restore.ipsw
iPhone 5s Model Number(s): A1457 ; A1518 ; A1528 ; A1530
iOS firmware file needed:
http://appldnld.apple.com/iOS8/031-05446.20140917.vuup2/iPhone6,2_8.0_12A365_Restore.ipsw
iPhone 6 Plus Model Number(s): A1522 ; A1524
iOS firmware file needed:
http://appldnld.apple.com/iOS8/031-05555.20140917.YWW0v/iPhone7,1_8.0_12A366_Restore.ipsw
iPhone 6 Model Number(s): A1549 ; A1586
iOS firmware file needed:
http://appldnld.apple.com/iOS8/031-05647.20140917.b0n9s/iPhone7,2_8.0_12A365_Restore.ipsw
2. Plug your device into your computer
3. Turn off the device by holding the Sleep/Wake or Power button and swiping it off
4. Hold the power button for 3 seconds
5. Begin holding the Home button without releasing the Sleep/Power button for 10 seconds
6. Release the power button and continue holding the home button until you get a popup from iTunes that your device is recognized as being in recovery mode.
7. Now hold down the (Mac Option/Alt) (Windows: Shift) Key and click on the Restore button. In the navigation sheet that appears locate the ipsw file you just downloaded and click Choose. Again, this will wipe out all the data on it so be sure to have a backup.
8. Be patient and wait for the installation process to be completed by iTunes
9. Once the restore is completed you can select your backup or treat the device as a new device.
Here’s another important note (which Windows users should pay particular attention to; also, this is something that only applies if the user chooses to look for the desired IPSW file on the Internet). Your browser may change the IPSW file into a .zip file. For example, Microsoft’s Internet Explorer does this, if used to download the firmware bundle. This doesn’t mean it’s unusable. Instead of wasting time switching web browsers, just rename the file to end in “.ipsw” and iTunes will accept it.