Telephony Audits require a skillset, knowledge base and background in PBXs installation, maintenance not just programming and use. Then, you must understand the billing, inventory, interworkings of what you are looking at- otherwise the audit is pretty much useless. So what, you see the bills, now what ?
1. Get the output records from the SMDR/CDR port and access to any reports on-site or via third party that the customer has in use.
2. Get access to the telephone billing for the past 6 months- all of it.
3. Get ALL the vendors involved surrounding the phone system.
4. Get the configuration and inventory of everything around the phone system.
5. Talk to the customer, get the scoop.
6. Modems and Maintenance codes are a big source of telephone (PBX) fraud.
7. The primary carrier should be able to implement enforced and validated account codes (7 digits length)
8. Have a meeting of the minds and id the source with the info- you need to understand billing and have some knowledge of HOW the phone system is operating.
9. Look into the VoiceMail system too for areas of security breeches.
10. Dial In - Dial Out. Features include call forwarding (off site), remote access, dial access codes, mailboxes, admin mailboxes, anything with a security code / password is subject to scrutiny.
11. Routing tables for custom call routing and least call routing are also subject to review- you must understand the basis of the decisions made and why to understand the routing in place.
12. Company policies and procedures - what are they ? What did they publish ? You'd be amazed as to what gets printed.
13. Nature of the company/organizations business. Understand it and you will understand, see, and know their "Traffic Patterns."
14. In hand tools- at the minimal: buttset, digit grabber, laptop with plenty of cables and types of cables - null modems and hyperterminal.
Hope this helps
The older I get, the less I know