We have a single Lync 2010 server. All users have there AD telephone numbers set as +61 2 9123 xxxx. We are using RCC. On the Lync client when USER A checks the contact card of USER C he see's the work number as  xxxx.When User B checks the contact card of User C he see's the phone number as +61 2 9123 xxxx . Why is this hap

If numbers are already in E164 format then normalization rules should not come in to play. Possibly User A has a bad cache of the address book. Try deleting .lsabs, .dabs, GalContacs.db and GalContacts.db.idx cache files from %userprofile%\AppData\Local\Microsoft\Communicator\sip_<username@domain>\ (exit Lync first).

If normalisation is coming in to play it is done with Company_Phone_Number_Normalization_Rules.txt. Rules in this file will allow AD numbers to be normailised when added to the Lync address book. Check for any normalisation errors in the Invalid_AD_Phone_Numbers.txt text file - \\LyncShare\1-WebServices-1\ABFiles\00000000-0000-0000-0000-000000000000\00000000-0000-0000-0000-000000000000\Invalid_AD_Phone_Numbers.txt

These articles may be helpful:

http://y0av.wordpress.com/2012/02/23/normalize_ad_numbers/
http://blog.schertz.name/2010/09/updating-the-lync-2010-address-book/

The problem is that its not with one user.We have lot of users  with the same problem.

Also I am now logged on to a another machine  and I have duplicate numbers.Want to know how the address book gets updated on the client machine.

book

The Lync client periodically downloads the address book via the internal or external web services. Try on one workstation to delete the client cache and see if it populates the same information. If it does then something isn't right on the server end.

If the later check the Invalid_AD_Phone_Numbers.txt file for errors.

You could also delete the address book files from the server \\LyncShare\1-WebServices-1\ABFiles\ then run

Update-CsUserDatabase (Synchronizes data between AD and Lync backend DB)

Wait at least 15 minutes

Update-CsAddressBook  (Writes changes in backend DB to the address book files)

This will regenerate all you address book files.

When you do the test, please check the Personal information manager is set to Microsoft Exchange or Microsoft Outlook. As Lync can search contact from outlook contact.

Please check there are no stale outlook contact for number XXXX.