exten => 1002,1,NoOp(${CALLERIDNUM}) 
exten => 1002,2,GotoIf($[ ${CALLERIDNUM} = 1003 ]?10:20)
exten => 1002,10,Macro(sipdial-assistant,${EXTEN},1003)
exten => 1002,20,Macro(sipdial,${EXTEN})