On the chance that my experience might prove helpful to others let me describe the scenario:
Axon as Local PBX
Single input line from Callcentric
Input line rings on group 701
Group 701 has two extensions, 101 and 102
Express Talk on each of two PCs, successfully registered with Axon as 101 and 102.
Express Talk enabled as a video phone (irrelevant whether "Receive Only," "Video Device" or "Screen Capture" selected.
Call placed from cell phone (PSTN) to Callcentric number.
Both extensions ring simultaneously.
When answered by either extension, the call is IMMEDIATELY disconnected.
Some other behavior.
Calls from one extension to the other behave correctly (with any video option or none at all)
Unchecking "Use ExpressTalk as a Video Phone" results in the extension being able to successfully answer the incoming PSTN call
If a call is initiated from an extension to a PSTN number it successfully connects regardless of the Express Talk video setting. In my case there was no video, however, since my cell phone doesn't support it.
Finally, and most puzzling, if instead of using a group to ring incoming calls on several extensions, the incoming line is rung directly to the extension, the video setting is irrelevant and the call will connect successfully.
Callcentric specifically states that they do not support video to PSTN calls and will not investigate scenarios involving this situation.
After nearly twelve hours of experimentation I have concluded that for my own purposes:
To ring on a group since I need that capability.
Disable video on the Express Talk phones to avoid the problems associated with immediate disconnects.
Hope this helps others avoid tedious experimentation and hair pulling over seemingly inconsistent results.
