You support a customer whose network environment includes Microsoft Lync Server 2013 Enterprise Voice deployed at two sites named Sitel and 5ite2. All users require extension dialing. Only direct…

You support a customer whose network environment includes Microsoft Lync Server 2013 Enterprise Voice deployed at two sites named Sitel and 5ite2. All users require extension dialing. Only direct inward dialing will be used for auto attendants or response groups. The extension numbers in four-digit format are stored in the telephoneNumber attribute on the users' Active Directory Domain Services (AD DS) account. Sitel uses 2xxx extensions, and Site2 uses 3xxx extensions. You want to retain the four-digit extensions in Active Directory, but also present the numbers as valid numbers in the Lync 2013 client. You need to ensure that four-digit dialing normalizes properly in the address book for Lync. What should you do?