i don't know how your billing application works but you should see connections to something like: b00205701017 that is how a conference bridge is identified in CCM, if you thru a trace you will see that before the conference is established all the parties involved call to that number. if you see which parties call to that kind of numbers you will see who was in the conference.
HTH
javalenc
if this helps, please rate
HTH
java
if this helps, please rate