Sends an MWI request to CallPath.
Use this custom server function to send an MWI setup request to CallPath (STLPIND call using indicator_code = STL_MESSAGE_WAITING).
For example, for AT&T, you might code the following:
SendData(Set_MWI)
number(34142)
mode(0)
duration(0)
LED_frequency(0)
timeout(10)