Just in case anyone found a miracle fix: Got some Radio Shack powerline intercoms here, article number 43-3106 but not sold anymore. Looks similar to this one but white:
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Whenever the new DECT phones ring the thing goes berserk. Loud beeper turns on and cannot be shut off anymore except by a power cycle. So I assume they screwed up the circuitry. Don't want to have another science project but if anyone fixed it and it's a simple matter of "putting a cap here and there", I'd do it. Else I'll just cut them loose.