do u need to be bidirectional like a phone, or to change the direction of the speech...eg u speak, u push a button and then u listen to what the other says?
and another thing, how many niles can u use between the corespondents, 2 3, or 4?
i have something. u need two normal phones, old ones work 2(the ones with the weeal) and some zenner diodes, a few resistors, and 2 buzzers and a 9v batt. it works fine.....
if u want i can give the schematic, i designed it long ago, so i wont try to find it if u dont want it