Dear Friend
Firstly You must put into consideration ou have a voice gateway and CUCM ( BE3000) , firstly you have to select protocol (MGCP or H323) , i recommend H323 to allow yu watch the debugs on your voice gateways . Be careful when you set yur DNs for cisco ip phones ( for end users) you have to put into your consider that your DN be included in the DID number , for example if you have user A who will have a DID 337567001 so i will give user A ext 7001 , it will make easy when you configure that translation rules and will make your configuration easier , Anyway good , Please rate if this helpfull.