Mine

exten => 18478971337,1,Macro(voicemail,${MATT},100)


[macro-voicemail]                                       ;Macros
exten => s,1,Dial(${ARG1},20,)
exten => s,2,GotoIf($["${ARG2}" != ""]?s-${DIALSTATUS},1)
exten => s,3,Hangup

exten => s-NOANSWER,1,Voicemail(u${ARG2})
exten => s-NOANSWER,2,Hangup

exten => s-BUSY,1,Voicemail(b${ARG2})
exten => s-BUSY,2,Hangup

exten => _s-.,1,Goto(s-NOANSWER,1)