Harry,

I modified it (and tested it) into a class. Here it is. Let me know how things turn out.

DEFINE CLASS Dialer AS CUSTOM

  nPort = 0
  #DEFINE GENERIC_READ  0x80000000
  #DEFINE GENERIC_WRITE 0x40000000
  #DEFINE CF_TEXT CHR(13) + CHR(10)

  FUNCTION DialNumber
  
    LPARAMETERS PhoneNumber, CommPort
  
    DECLARE INTEGER WriteFile IN Win32API;
      INTEGER hFile, STRING @lpbuffer,;
      INTEGER nNumberOfBytesToWrite,;
      INTEGER @lpNumberOfBytesWritten,;
      STRING @lpOverlapped
    DECLARE INTEGER CreateFile IN Win32API;
      STRING @lpFileName, INTEGER dwDesiredAccess,;
      INTEGER dwShareMode,;
      STRING @lpSecurityAttributes, INTEGER dwCreationDisposition,;
      INTEGER dwFlagsAndAttributes, INTEGER hTemplateFile
    DECLARE INTEGER FlushFileBuffers IN Win32API;
      INTEGER hFile
    DECLARE INTEGER GetLastError IN Win32API
    LOCAL lnport, lnwritten, lcmnd,;
      lcport, lnresult
    lnresult = 0
    lcport = CommPort
    lnport = CreateFile(@lcport, GENERIC_READ + GENERIC_WRITE, 0, 0, 3, 0, 0)
    IF lnport > 0
      This.nPort = lnport
      lnwritten = 0
      lccmnd = "ATDT" + PhoneNumber + CF_TEXT
      IF WriteFile(lnport, @lccmnd, LEN(lccmnd), @lnwritten, 0) # 0
        * Flush the buffer to assure the data was written
        = FlushFileBuffers(lnport)
      ELSE
        lnresult = GetLastError()
      ENDIF
    ELSE
      lnresult = GetLastError()
    ENDIF
    RETURN lnresult
  ENDFUNC
  
  FUNCTION HangUp
  
    DECLARE INTEGER CloseHandle IN Win32API;
      INTEGER hObject
  
    LOCAL lccmnd, lnresult, lnport, lnwritten
    STORE 0 TO lnresult, lnwritten
    lnport = This.nPort
    lccmnd = 'ATH0' + CF_TEXT
    lnresult = WriteFile(lnport, @lccmnd, LEN(lccmnd), @lnwritten, 0)
    IF lnresult = 0
      = FlushFileBuffers(lnport)
       * Close up
      = CloseHandle(lnport)
    ELSE
      lnresult = GetLastError()
    ENDIF
    RETURN lnresult
  ENDFUNC
ENDDEFINE
SET PROCEDURE TO Dialer ADDITIVE
* Useage
oDialier = CREATEOBEJECT('Dialer')
RELEASE PROCEDURE Dialer
IF oDialer # NULL
  ? oDialer.DialNumber('5555555', 'COM1')
  ? oDialer.HangUp()
ENDIF

Note: I did have some problems if the line was busy, but the code above seems to work as advertised.