asterisk users - Oct 2005 - play a voice file voice for " decline "

When get sip respond 6xx ( such as 603 decline),  I want asterisk to
play a voice file to the caller,  how to do this in extensions ?

for example, when get 603 respond,  play  decline.gsm  to caller
                   when get 604 respond, play doesnot-exit.gsm  to caller
                    when get 606 respond , play not-acceptalbe.gsm to caller







SIP response codes, class 6: Global failures


600 Busy Everywhere
603 Decline
604 Does Not Exist Anywhere
606 Not Acceptable