Able to answer—but not make—iPhone calls on Mac Background
Among the many promising features of OS X 10.10 grouped under the label &quot;Continuity&quot; is the ability to make and answer iPhone calls from the Mac. The Mac uses the iPhone's connection to the carrier's voice network. I think this technology works over wifi.
Problem
I'm able to answer calls, but not make them. The error message I receive on my Mac is, &quot;iPhone calls not available. Your iPhone must use the same iCloud and FaceTime account.&quot;
What I've done
I've confirmed that both iCloud and FaceTime on my iPhone—as well as iCloud on my Mac—are logged into the same account.
Question
What could be causing this issue, and what should I do to fix it?
Try completely logging out of your Apple ID/Account, everywhere (every setting/option where you can do so), on both of your devices.

For example, on iOS, you should try signing out from iCloud, iMessage and FaceTime:


Settings → iClound → Sign Out
Settings → Messages → Send &amp; Receive → Apple ID: ... → Sign Out
Settings → FaceTime → Apple ID: ... → Sign Out


Then try logging back into your Apple ID/Account on them and setting it up again.

Hope this helps :)

-James