OK here's an update. I disconnected the phone line to the HR24-100 and the repeated DTV home calls stopped. Since the HR24-500 was not initiating calls, I purchased a PPV. Finally after about a week the 500 made one single DTV call home Saturday and apparently reported the purchase as the length of the call was 2+ mins. Since I had not experienced difficulty with DTV home calls for 1.5 years, I did not expect a failed call from the HR24-500.
So now either the HR24-100 is defective or there is a problem between it and my phone hub/patch panel (though the caller ID works fine). My phone lines are all home run (star) configuration w/Cat5E using 3 pairs to each RJ25 jack. Though the line to the HR24-100 sounds good, I'll plug in a 3 line telephone splitter and switch pairs to the 100 to see if that helps. BTW, beware of those with their microcosm experience applying it to everyone else. About 1.5 years ago I came to this forum asking participants using VOIP if they had any trouble supporting DTV dial-up data service. The general consensus was that it does support it without issues. My VOIP using G.711 always tests to MOS 4.2, zero packet loss, and jitter < .5 ms - - that's about as good as it gets on a channel almost half way across CONUS and it will easily support the low speed FSK data stream. Other VOIP codecs using compression algorithms may have issues. I was a Technical Controller for 15 years and did extensive voice-grade channel QC tests. There is a limit to the voice-grade modem speeds via VOIP, as compared to T1 derived PCM channels, predominately due to the phase jitter.