Of course I think I've figure it out after I posted to the listserv. Sorry for the extra message, but for anyone googling, check out the following flag: S - Simplex Dumb Phone Control mode. This allows a regular phone user\n" transmitter is toggled on and off when the phone user presses the\n" funcchar (*) key on the telephone set. In addition, the transmitter\n" will turn off if the endchar (#) key is pressed. When a user first\n" calls in, the transmitter will be off, and the user can listen for\n" radio traffic. When the user wants to transmit, they press the *\n" key, start talking, then press the * key again or the # key to turn\n" the transmitter off. No other functions can be executed by the\n" user on the phone when this mode is selected. Note: If your\n" radio system is full-duplex, we recommend using either P or D\n" modes as they provide more flexibility.\n"