Actually the current version in the CUCM in 8.6.2, and we have to upgrade to version 10.5.2. In the NICE lab we have version 10.5.2 also as well in the lab NICE and this version 10.5.2 works perfectly between Cisco Phones internal callas. However, we havent put in the live new version because the NICE PARTNER. They say that the NICE Vendor won't support version 10.5.2 yet, and we are waiting for them in order to upgrade the call manager.(Their exactly words we won't support the SIP Trunks yet).
Can you check this information with your NICE Partner.
Regards
Wilnes