I've asked a similar question recently and got the answer I was looking for but still have a bit of a predicament.
In the call centre, agents take calls from technicians who sell new business to clients, they give all the information over the phone and we provide them with a lead ID as a reference. When we convert the lead into an opportunity (unless on a report where I can match the Lead ID to the converted opportunity) there is no way that I can find to discover the original lead information.
Basically what I am asking is, Is there a way to still have the lead information active on Salesforce? So if a query arises about the opportunity, we can go back to the lead page with all the information on as if it was freshly taken from the technician on the phone (before conversion)?