It wouldn’t work on a genuine Hayes modem - those would only listen for commands if there was a pause, +++, another pause, and then the AT command. Hayes’ paten

It wouldn’t work on a genuine Hayes modem - those would only listen for commands if there was a pause, +++, another pause, and then the AT command. Hayes’ patent was actually on the pause itself (in-band signaling was already well-known), so the off-brand modems wouldn’t implement it, while still implementing the “Hayes-compatible” command set. Those are the ones you could get to hang up if you could trick the program on the other end into echoing the string “+++ATH”.