asterisk users - Jan 2005 - Playing a file upon pickup (dial command?)

Hi,
I'm trying to do the following but can't quite get it right:

1) Callers rings DID number
2) Asterisk rings the appropriate channel for 30 second, if no answer sends 
to voicemail (no problem up to here, of course)
3) IF the channel is answered Asterisk plays an audio file
4) Asterisk connects caller with me

I need to do this to "cover up" the delay within the first few seconds
of a
phone call.
Ofter I find that I only hear callers when they've obviously been saying 
"hello" for a few times
(can tell from their tone of voice!). I think that if I could play an audio 
file (but only if I pick up the phone,
to avoid costing money to callers) in the first 2 or 3 seconds they would at 
least know that
their phone call has been answered. It would be a sort of echotraining!

I've tried different solutions but I cannot get a file to be played AFTER I 
answered the channel.

This is more or less what I'm trying to do:

exten => 301,1,SetLanguage(en)
exten => 301,2,SetMusiconHold(default)
exten => 301,3,Dial(SIP/301,5,tr)
exten => 301,4,Playback(transfer)
exten => 301,5,VoiceMail,u1234
exten => 301,105,VoiceMail,b1234

Is it possible, or am I asking too much from Asterisk?
Thanks to all,
manny