Help with Very Specific Information Tracking

[SaultTribeIT]

Hello all,
I'm brand new to Zabbix and very excited to get my organization using it to it's full potential. We are trying to outsource a clunky, expensive product with this and so far only have 1 question from our Telecom department that I cannot answer. Here's the situation:
Our Telecom department uses our current solution to track all kinds of information from our switches including which Department is using each port so they can run a report each month to bill out services. I can not find a good solution for this yet in Zabbix. I figured I would need to create a custom item and add it to the template, but I've never had to create a custom item before so I'm a little lost. I'd be very grateful if someone with some experience in creating custom info fields could help me out.

Thank you very much!

[SaultTribeIT]

It is currently an SNMP query, which is using the SNMP v3 and CISCO IOS SNMP linked templates, but with some customizations to pull specific port information and other granular data. Would a Discovery Rule work in this situation if the information is not stored on the switch? In this instance, the information would need to be user inputted, but still be able to have reports run against it that essentially tally's up all instances of a specific number (Business Unit Identifier) for quick and easy billing.