I don't deal with licensing, but AFAIK, SME can simply be attached to your PLM that handles CUCM, and that would be it, or there should be a standalone license, if you wish to use the co-res PLM from your SME, that only gives you a few phones so that it doesn't complain about licensing, but it would be the same as asking for 5 user licenses for a regular CUCM on which you will register phone. I have no idea how many users come with the license, just said 5 as an example.
http://docwiki.cisco.com/wiki/CUCM_FAQ#How_do_I_license_my_SME.3F.3F
HTH
java
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