Mine

[localusers]
exten => 7777,1,Goto(callback,s,1)

[callback]
exten => s,1,Wait(1)
exten => s,2,Answer
exten => s,3,Background(thisisacallback)
exten => s,4,DISA(no-password|localusers)

the .call
callerid: 08703005030
extension: 7777
channel: Local/1001
context: localusers
priority: 1