[Context]
exten => _X.,1,Log(NOTICE,Dial Status of ${EXTEN}: ${SIPPEER(${EXTEN},status)})
exten => _X.,n,GotoIf($["${SIPPEER(${EXTEN},status):0:3}"="OK "]?ok1:NEWCONTEXT)
exten => _X.,n(ok1),Log(NOTICE,Calling number is available)
exten => _X.,n,Dial(SIP/${EXTEN},50)
exten => _X.,n,Hangup()
exten => _X.,n(NEWCONTEXT),Goto(NEWCONTEXT,${EXTEN},1)
exten => _X.,n,Hangup()
[NEWCONTEXT]
exten => _X.,1,voicemail(${EXTEN}@Context)