Type          : 54
 Name          : Send an on-line message
 Optional Data : None

   Allows  the  user to send a message to another user  who  is
   logged on to  another line at the same time.  Provided  that
   the  other  user has not set his/her "do not disturb"  flag,
   the  sender  will be prompted for a one-liner  to  transmit.

   Depending on what the recipient is doing at the time, he/she
   will get the message ten to fifteen seconds later.