Hi, the licensing model from 4.x to 5.x versions has changed. With 4.x you have an ip phone with its license but with 5.x you have the concepts of "device license units" and depending on the model you'll need less or more licenses.
I recommend the reading of next url:
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_qanda_item0900aecd805009fc.shtml
An after you can use a cisco tool that it's going to tell you what exactly you need, the solution expert tool:
www.cisco.com/go/sx
Regards.
Hope this help you, if so pls rate the post.