Jabber for Windows & Mac assumes that the sAMAccountName & userPrincipalName in Active Directory provide the correct username. However if in CUCM you're using the telephoneNumber or ipPhone field as the username (which I've seen many times!) Jabber won't work properly. When you view a contact in Jabber the IM address will show the incorrect username, for example firstname.lastname@example.org instead of email@example.com.
In the days of CUPC you could edit the LDAP attribute mappings in the CUPS GUI, but for Jabber you have to create an XML file to configure the attribute mappings. Assuming you're using the telephoneNumber field as the username, create a file in UTF-8 encoded text file named jabber-config.xml containing the following:
<?xml version="1.0" encoding="utf-8"?>
Upload this file to all your TFTP servers & restart the TFTP service on them. Now when Jabber loads it will download this file & assign the correct LDAP attribute mappings.
There's a bunch of other settings for Jabber that you can only configure via an XML file, fortunately Cisco have released a tool to help automate this process.