Hallo!
Versuche folgendes:
exten => 99,1,NoOp(${EXTEN})
exten => 99,n,ChanIsAvail(SIP/testphone,s)
exten => 99,n,NoOp(${AVAILSTATUS})
exten => 99,n,GotoIf($[ ${AVAILSTATUS} = 3 ]?busy:no)
exten => 99,n(no),Dial(SIP/testphone,300,r)
exten => 99,n(busy),Goto(std-local,9999,1)
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