[Asterisk-Users] Silently Wait for DTMF Input

[asterisk at bortal.de]

Hello!

I would like to call a number (e.g.35), and when i press a secret code
(12345), it should jump to my voicebox menu.
On this page http://www.voip-info.org/wiki-Asterisk+cmd+background i found
something about "Silently Wait for DTMF Input".
In my case it wouldn`t be silence. It woudl just play the away message.

Now how can i include such a secret code to my background funktion?
I am looking for something _like_ this:
   exten => s,1,Background(away,12345,voicebox_35)

If someone presses 12345 whilest the away message is playing, it jumps to
the voicebox_35 context.
Know what i mean?!
A quick link to the needed docu or some tips/examples would be great!

Thanks, Mario