i have got an issue .. i configured IP Phones for one of my customer .. they have one PRI .. whn some one call to those ip phones from outside,some time they hear tone like Fax tone or tone like internet is connectd and some time they can call without any problem .. so how should i trouble shoot this issue !! can any one help me ... i gues this would be issue from service provider but how can i make it sure from my side !!!!