The simplest thing to do is to use different queues for different customers, though you may have the same set of agents working on all queues at once. This will make the separation trivial.
The second simplest thing to do is:
- rewrite the caller-id of the incoming traffic to prepend a code that tells either the customer or the DID, like from "(555)5551234" to "01-(555)5551234", where 01 is the customer or the incoming DID
- use QM's Area analysis to break down calls based on the first two digits of the caller-id.
See also:
http://queuemetrics.com/faq.jsp#faq-027-did_tracking