There is a special feature in the dial plan for the case where the user must dial an access code
to get an external line. A digit followed by a “,” will cause secondary dial tone to be
generated. For example, assume a rule “9,xxxxxxx” is added. When the user dials 9, the
phone will generate secondary dial tone. Then, when 8 digits have been dialed, they will all
be sent to the server.