exten => 3715,1,Answer
exten => 3715,2,GotoIf($["${RDNIS}" = ""]?4)
exten => 3715,3,MailboxExists(${RDNIS}@default)
exten => 3715,4,Directory(default|internal)
exten => 3715,5,Hangup

exten => 3715,104,VoiceMail(u${RDNIS}@default)
exten => 3715,105,Playback(vm-goodbye)
exten => 3715,106,Hangup