Here is the TechNet link for Understanding Name Lookups from a Caller ID
In that above TechNet link you can find very good information and flow chart about Name Lookups from a Caller ID.
With this Blog I want to make it simple and add some more information.
Unified Messaging (UM) uses information about the calling and called parties to perform a name lookup. This lookup enables a caller's name to be included:
If you have UM enabled users they call each other or leave Voice message, you can see their name as a Caller ID and get to know who called you.
What happens if you have users who are not enabled for UM and if they try calling UM enabled user or Leave voice message?
In this case we have following options to display NON-UM enabled users Caller ID.
1) You can have NON-UM enabled user phone number (how your UM server is receiving) in your outlook contact list.
This is very difficult task to ask all your UM enabled users to add all NON-UM enabled users in their outlook contact list. So I prefer Step 2.
2) Add NON-UM enabled users Phone number (how your UM server is receiving) to msRTCSIP-Line attribute.
Here are the Steps to achive this.
· If you have OCS already installed in your environment then I assume all your users are enabled for OCS. If so go to NON-UM enabled user properties in OCS console and click on configure button. Enable the user for Enterprise voice and enter that user’s phone number in Line URI as tel:+number.
This will intern update msRTCSIP-Line attribute in AD.
· In case your NON-UM enabled user are not OCS enabled or if you don’t want to enable that user for enterprise voice, you can enter the phone number directly at msRTCSIP-Line attribute.
Either way you have to at least extend the schema for OCS. Then only you can see msRTCSIP-Line attribute for the users.
If you want add phone number from AD, Go to ADSIEDIT.MSC and locate the user properties in domain partition.
Look for msRTCSIP-Line attribute and click on edit. Enter the phone number like tel:+number.
Hope this helps.