CompuServe Messages

It used to be a telephone system standard that the battery polarity at the calling phone would REVERSE when the other end answered. I gather that the purpose was to allow pay phones to collect your dime (how's that for nostalgia?) … I wondered if perhaps some modems might try to use this phenomenon to see if a connect has taken place .. or key carrier, or something. Again, though .. I haven't tried it, since my modems chug along happily with no DC voltage supplied on the wires. –Jim