Microsoft offers two different ways to get at the data I was looking for. Either from a web browser on the Lync 2013 Reporting Server or from Lync Front End Server via PowerShell. For us it was easier to go with the browser based report.
To begin, log into your Lync Server control panel and under Top Actions, expand the View Monitoring reports section and click on your server.
Attachment 1
From there, the Monitoring Reports section will appear. Assuming your user account has the correct priviledges, then the nexxt step is to click on the IP Phone Inventory Report link under the System Usage Reports section.
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Finally the IP Phone Inventory Report will appear. Change the dates and other filters as desired and click on the View Report button in the upper right corner.
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Note that this tool will gather data on the following areas: Manufacturer, Hardware Version (this seems to include Make/Model/firmware version), MAC address, User URI (the person who has logged into the phone), User agent (appears the same as Hardware version), Last logon time, Last logoff time, and Last activity.
A couple of notes that I've found and also mentioned by Microsoft:
This report considers something within the From/To date as when the phone was last logged in with. Meaning if you run a search from April through August, you will only find devices that have been logged into since April. If there is a device that was logged into in March and stayed logged in, this will not be picked up by the report. In this regard, it's likely best to run the report for a longer timeframe than you might need and export the file to CSV and remove unneeded entries.
Another thing I've noticed is that you may have multiple results from the same phone. I noticed that when I sorted by MAC address, I had plenty of phones appear 2-3 times. This is because the phone was first logged into with an earlier firmware and subsequently had a new firmware installed, which the phone considered itself logged into again creating the second entry.
