You are correct that your investment in CME phones will be protected if you upgrade to CCM at a later time. Have a look;
Q. I have a Cisco Unified CallManager Express (CME) customer who wishes to upgrade to Cisco Unified CallManager 5.1. What steps do I need to follow to ensure the licensing transfers?
A. Do the following:
1. Determine how many and what type of devices are on the customer's Cisco Unified CME.
2. Enter the quantity of each device in the "yellow" cell in the Cisco Unified CallManager Device License Unit Calculator pasted at the end of this document.
3. Contact firstname.lastname@example.org with the MAC address of the publisher and the number of device license units calculated in step 2. The customer does not need a node license-it comes with the new Cisco Unified CallManager.
These are the paths to get to each CCX logs through CLI. They may be helpful if you are having issues accessing RTMT or downloading logs through it.
If you want to download them you have to prefix "file get " and you can add one of the options (re...