there are little circuit boxes that immitate the phone line, last I saw
one about 60 bucks

Thats the way to go... Getting the operating voltage (48vdc) isn't that
hard just hook up 4 12 volt batteries in series with an 800 ohm (If I
remember correctly) reisistor on the end. Getting a 20hz ringtone is the
difficult part since the wall current is 60hz.. I never figured out an easy
way to make my phones ring.

- Mike