Need a voice audit tool

If such a thing exists. I'm doing VOIP/data networks and in order to do a decent feature match, I need to know what the customer has currently. Unfortunately, customers rarely have this documented and it's difficult to decode this from a legacy phone switch.

So, the question is, is there something that will crawl a legacy voice network and audit extensions and features available? Something that will interrogate the PBX, maybe?

Any suggestions?