Thanks for your help. Definitely getting there, although we haven't quite crossed the finish line. It (FaceTime) now dials out; you can hear through the iMac repeated rings (4 or 5). However the receiving phone line, for example my Landline or my friend's Android cell, does not ring/recognize that there's an incoming call. After listening to the iMac's audible repeated outgoing "ringing," I then hear nothing (non-response) and the iMac displays the message "Call Failed."
I realize that what I initially stated may well be irrelevant, but to repeat, I recently changed cell phone carriers (Comcast Xfinity to Consumer Cellular.) It occurs to me that that is when the problem started. Could that be part of this conundrum?