Hi Leung,
Your investment in CME phones will be protected if you upgrade to CUCM . 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 licensing@cisco.com 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.
From this excellent licensing doc;
Cisco Unified CallManager Licensing
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_qanda_item0900aecd805a7062.shtml
Hope this helps!
Rob
EDIT: sorry the site won't let me attach the doc right now it is in this thread;
https://supportforums.cisco.com/message/1130764#1130764
