If you just updated your new iPhone 6 or 6 Plus, you've probably noticed your cell service and TouchID have died a swift death. But fear not! There is a way to downgrade back to iOS 8 and restore full functionality while Apple patches the update. Here's how to do it.
Of course, doing this will delete everything off your iPhone. But if you need cell service for any reason before Apple takes care of the bug, it's pretty much your only option.
Backup to iTunes or iCloud.
With you phone plugged into your computer, open iTunes to the device screen. Make sure you have This Computer selected and hit Back Up Now.
Download the iOS 8.0 firmware.
Go to this website. Enter your device, the model, and under the firmware menu, pick iOS 8.0. Then plug your phone into iTunes, and with the device window open, hold alt/option for Mac and shift for Windows while you click Restore. Next, select the .ipsw file you just downloaded, and wait while your phone wipes itself clean.
Do not restore from a backup at any point.
Yes, you will lose all your photos, text messages, music, what have you, but restoring that stuff also mean choking your service. You can get it all back from the backup you made initially once Apple has fixed the update. So remember, this is just temporary—we hope.