So many ways to skin this cat. Does your tele team use statuses? If so, you may be able to use those statuses to measure success.
For example, when they are calling, do they put a lead in a status like "Attempting Contact?" If they actually progress the lead, would you consider that a Success? Maybe they use some link of "Connected" or "Verified" status?
If above is true, you could use a Change Data Value trigger based on Lead Staus changing to a new staus of "verified"
Of course, if the list contains a bunch of Contacts, this process might not work.