I am able to make and receive phone calls from my MacBook running Yosemite via my iPhone when I am only connected via WiFi to my home network (Airport Extreme).
When I connect additionally via my Thunderbolt Ethernet adapter to the same network it does not work anymore. Making and receiving phone calls always fails with the message "Call failed" after trying for some seconds to connect to the iPhone.
UPDATE: I can see the following error in the console:
17/10/14 14:15:23,082 discoveryd: Basic Network GetExtendedFlags ioctl failed Device not configured