That's usually a function of the conference bridge. Are they using the built-in MEET ME CONFERENCE, the Mitel conference bridge, or one from someone else?
If you're using the built-in there's actually a "real time" CONFERENCE report under the CALL ACTIVITY tab of SYSTEM ADMIN & DIAGNOSTICS. My experience is that it is slow to refresh, but you can click on TOOLS icon and force a refresh.
Other applications will have much richer reporting, including historical.