What phone do you have?
Moto G5 plus
No issues with outgoing or inbound calls on wifi.
Can receive inbound calls fine on cellular .
Good cell signal (LTE 80% of full).
Getting fast busy on all outgoing calls via cell.
Not location sensitive – tried at three separate locations where I have had no issues in past (with LTE at 75%+ at each location)
Zipcode: 94121 (San Francisco)
Did the easy stuff - reboot the phone, refresh activation, etc.