Function:   AtModem()

               This function enables the user to send a command
               string to the modem. This function is used
               basically to enable someone to make the (Hayes
               Compatible) Modem dial for someone (voice). Other
               Clipper libraries provide specific COM support.

   Syntax:     AtModem(<cString>[,<nPort>])

   Arguments:  <cString> is the string to send to the COM port. a
               Carriage Return character is automatically added,
               so you do not have to provide it. <nPort> may be
               entered and must be a number between 0 and 3,
               indicating the COM port to use (1 to 4). If <nPort>
               is not given, COM1 is assumed.

   Returns:    Nothing. When the adressed COM port was not
               installed, the call is ignored.

   Usage:      * An example Dialing routine:
               Dtr(.t.)    && Set Modem in ready mode...
               AtModem('ATDT5551234;')
               * Dial using Tone dialing (ATDP is pulse dialing)
               * Note the terminating ';' ie. no CONNECT !
               Wait "Pick up phone and press a key.."
               Dtr(.f.)
               * When Dtr is On the conversation is echoed in the
               * Modem, Dtr(.f.) turns that off.