Da Voismart Knowledge Base.
Park and Announce

Park a call into the parkinglot and announce the call to another channel.

announce template: Colon-separated list of files to announce.  The word PARKED
                   will be replaced by a say_digits of the extension in which
                   the call is parked.
timeout:           Time in seconds before the call returns into the return
dial:              The app_dial style resource to call to make the
                   announcement.  Console/dsp calls the console.
return_context:    The goto-style label to jump the call back into after
                   timeout.  Default <priority+1>.

The variable ${PARKEDAT} will contain the parking extension into which the
call was placed.  Use with the Local channel to allow the dialplan to make
use of this information.