I am an engineer but with limited experience in telecom. I have yet to locate a cordless phone for residential use that can operate off the phone company's DC power source for any useful length of time so as to not require (at least for the base station)an AC connection for power. Does this technology exist to your knowledge? If not, are you aware of the barriers or obstacles to developing such a device, whether technical or because of regulatory issues? Thank you in advance for your consideration.

To my knowledge it does not exist, nor will it ever. The power necessary to operate the ringer, seaker and microphone of a regular analog phone is minimal. So a regular phone can draw on the power sent over the lines. But a cordless phone needs more power to operate the radio transceiver needed to connect between handset(s) and base station.

Nope, but it can easily be done and I do it at home.

A small UPS, actually about 500 VA (I got it free, needed a battery) is connected to the answering machine/base station, a small high intensity lamp, primary backup to a PERS alarm system (It also has it's own internal backup). The phone powers 4 cordless phones. It will power it for quite some time, as in hours.

It's recommended that at least one phone be available that does not require utility power.