Voicemail using an unexistant file!

Hi there! im currently in a problem, i need to put in a greeting a custom file that we received (in .wav format) i currently encodned it as GSM then the first idea was to go to the path /var/spool/asterisk/default/200 and then just move the file FILE.WAV and put mine but now asterisk it is using a *.slin file that i dont found where it is? any tip or trick how to do this?

– <SIP/9000-00000059> Playing ‘/var/spool/asterisk/voicemail/default/200/temp.slin’ (language ‘en’)
– <SIP/9000-00000059> Playing ‘vm-intro.gsm’ (language ‘en’)

thanks in advance!