If you really want to keep track of your participants, use a registration page for all of your conference calls.  Registration systems will record any data you want and store it for use later.  Also, during a live call, you can see the data next to that caller - speaking directly to users and knowing who they are increases the personal touch of your call (not to mention it is impressive).  Also, each participant receives their own unique code for the call - again, more personal.

After your live event, you have data on who registered, who attended the live call as well as who did not - great for follow-up.  For paid services like teleclasses, this is a great way for tracking attendance and keeping control of who gets it.  For required employee calls, the data will keep everyone accountable.

Best of all, it's free.  Try it out!