I have iOS 10 installed on my phone. As far as I can tell everything is configured properly. A number of support documents out there for iOS 9 list verifying that "Use cellular data" is enabled on the phone in FaceTime settings, however this is not an option in iOS 10.
I did verify under Settings > Cellular that FaceTime was indeed enabled.
Everything I've read online is that since Yosemite, I should be able to place phone calls to any telephone number using features from that release such as is outlined here: https://9to5mac.com/2014/10/19/make-phone-calls-from-your-mac-and-ipad/comment-page-1/
Unfortunately, most numbers in my Contacts app have the dial button disabled.
Both devices are on the same Wifi network (phone and macbook).
Update: I was able to resolve this by logging out of iCloud on my Mac in System Preferences and then logging back in. My device did not show up on Settings > Phone > Calls on Other Devices until I did this.
Best Answer
It's impossible to FaceTime to a non-Apple device. They both must have the Facetime app. (Middle East countries doesn't have the FaceTime app.)
Think of it like a Viber call: both parties need the app before one can phone the other.