As soon as iOS 8.1 hit two days ago, I immediately went about checking out a pair of new features I care about the most, Text Message Forwarding and iPhone Cellular Calls.
As a quick reminder, Text Message Forwarding lets me mirror text messages sent to my iPhone in the Messages app on the Mac or iPad. With iPhone Cellular Calls turned on, I can finally make and receive phone calls on my other Mac and iOS devices through my iPhone's cellular connection.
But something was amiss, or so I thought, because I just couldn't get either feature to work. While attempting to enable Text Message Forwarding, the system prompted me to enter a confirmation code my Mac was supposed to generated, but didn't.
Likewise, trying to enable iPhone Cellular Calls yielded a FaceTime error message saying my devices must use the same iCloud account, even though I was using FaceTime without any problems before.
Having spent a few hours restoring my devices as new, reseting network settings, changing settings on my router and checking the status of iCloud services, I eventually came to the same realization as did the other affected users: Text Message Forwarding requires you to use an email address and for iPhone Cellular Calls to work properly, FaceTime must be signed in with your Apple ID.