do you mean if the telco is connected to a VoIP gateway using something like ISDN or analogues lines?
If this is what you mean then there
is no direct way of finding out what equipment is on the other end.
Employees at the telco may call a number which is assigned to the ISDN/analogue lines. If the gateway had a calling card application associated with it then they would have an idea that some form of business was being run
using their lines.
However there is no way that their equipment can detect what equipment is on the other side.
If the gateway was sending calls out to the telco then there is a possibility that by analysing the CDR’s they may get an idea of what is going on. However given that residential and business users make many different types of call to many different destnations this may not be a problem. If however a very small company was making very large amounts of calls then this may be a giveaway.
However having worked for 2 European OLO’s in my experience we would have been happy to receive the traffic whether it came from a VoIP gateway or somewhere else.