Something

[macro-sipphone]
exten => s,1,Answer
exten => s,2,Wait(1)
exten => s,3,GotoIf($["${ARG1}" = "${CALLERIDNUM:6}"]?7:4)
exten => s,4,Dial(SIP/${ARG1},20,o)
exten => s,5,Voicemail(su${ARG1})
exten => s,6,Hangup
exten => s,7,Answer
exten => s,8,VoicemailMain(${CALLERIDNUM:6})
exten => s,9,Hangup

[sip]
exten => _40XX,1,Macro(sipphone,${EXTEN})