[walrus01]

incredibly inefficiently, and only for loads of 5-10W max... phone wiring is not thick enough in gauge and 12V has very high voltage drop over distance for any appreciable amperage.

there is a good reason why we use 110-240VAC to distribute power in houses.

[Johnythree]

The phone line is essentially "constant current". There's 48V before you draw current, but that quickly drops to zero when you lift the handset, because there's an exchange relay in series which senses when the phone is "off-hook"

[tardo99]

http://www.britishtelephones.com/howtele.htm

Is 16 ohms per thousand feet really that high?

[imgabe]

Yes. Typically devices can tolerate a voltage drop of about 3%. With that resistance, a 1A load can only go 22.5 ft from the source. Considering you might have to run up a wall, across the ceiling and down another wall, you might not even get to the opposite side of a room.