[mediant]
exten => 262358298,1,Set(CallBackNumber=${CALLERID(number)});
exten => 262358298,n,Ringing()
exten => 262358298,n,Wait(120)
exten => 262358298,h,DeadAGI(agi://127.0.0.1:20203/agi_handler_callback?callerid=${CallBackNumber});