Mine

exten => 1234,1,Dial(SIP/1234)

exten => 1234,102,Set(OLDEXTEN=${EXTEN})
exten => 1234,103,Background(pres-star-one-for-callback)

exten => *1,1,DBPut(CALLBACK/${OLDEXTEN}=1)
exten => *1,2,DBPut(CALLBACK2/${OLDEXTEN}=${CALLERIDNUM})


exten => h,1,DBGet(CB=CALLBACK/${CALLERIDNUM})
exten => h,2,DBGet(CB2=CALLBACK2/${CALLERIDNUM})
exten => h,3,GotoIf,"$[X${COUNTER} = "X"]?5:4"
exten => h,4,System(...create call file use CB and CB2)
exten => h,5,NOOP()