probleme réglé, il fallais ajouter un fichier astsms.conf


[astsms]
exten = _.,1,NoOp(SMS receiving dialplan invoked)
same = n,NoOp(To ${MESSAGE(to)})
same = n,NoOp(From ${MESSAGE(from)})
same = n,NoOp(Body ${MESSAGE(body)})
same = n,Set(SIP_USERNAME=${EXTEN})
same = n,Set(SIP_ADDRESS=${SIPPEER(${SIP_USERNAME},ip)}:$ {SIPPEER(${SIP_USERNAME},port)})
same = n,MessageSend(sip:${SIP_USERNAME}@${SIP_ADDRESS},$ {MESSAGE(from)})