I'm getting the following message when I start CUCM:

The system is operating with an insufficient number of licenses. If additional licenses to cover the shortage are not configured in your Cisco Prime License Manager within 59 days, you will no longer be able to provision users and devices.

In the Cisco Prime License Manager, I get the following:

Enhanced Plus (10.x) - Unified CM

The product instances require 1 licenses but only 0 are installed or available to be borrowed from an upper license tier.

How can I find the device (I'm sure it's a phone) that causing this to happen?

Many thanks!!!