I don't know if you have been going through this problem.
Many clients that have acces to Internet through ADSL service are having their phone/voice lines busy because an external user through Internet takes their lines to make world wide phone calls, charging this cost to the ADSL user.
The fraud is related to the way the hacker takes the gateway that belongs to another user in another country and provides phone services.
PLease let me know if you have heard about this. Is there any vulnerability?
Thanks in advance.