Yup I'm having a similar problem to you all. Here's my situation:
- iPhone 5s (iOS 8.1) with AT&T and Macbook Air (mid 2012, OS X Yosemite)
- Handoff works great
- Phone call Continuity does not work
- If I try to make a call from my macbook air (e.g. contacts card with little blue phone icon [not face time]), the little black box for FaceTime phone calls on the top right appears and says "(Contact Name) ..... Using Your iPhone" with the option for Video (grayed out), Mute, and End. But almost immediately afterwards will say Call Failed with the option to Close or Retry
- I had an incoming call once that went to my macbook air, I actually didn't answer because it was inconvenient to at the time. Although I've had other incoming calls on my iphone, none went to my macbook air except that one time. Weird.
- It seems that Phone call Continuity is established and wants to function up until actually initiating a call.
- Typical settings are all correct, to my knowledge (i.e. FaceTime, iCloud, Apple ID, Allow iPhone Cellular Calls, WiFi network) and have tried signing in/out, restarting, and in different chronological order.
- Called Apple Support, spoke to 3 different people, two of which knew very little about Apple (e.g. asked me if my device was a 'Mac Air', asked me to turn on airplane mode on my laptop device, asked me to turn on airplane mode on the iPhone which I was using to call him....). The third asked me to wait for iOS 8.1, which hasn't helped.
- Went to Apple Store, they couldn't figure it out and said they'd elevate it to an Apple Engineer and I was suppose to hear back today, but have not.
I'm basically at a wits end. This is nuts. Over a function that I probably won't use a lot. But it's the principal of the thing, it's supposed to work! Hahah. I'm glad I'm not alone in this problem. Hopefully a fix can be found.