Users with Microsoft Lync 2010 clients can place calls by typing a name or phone number on their keyboard, or using a dial pad displayed on their screen. Users can also initiate calls directly from their Contacts list. You can also deploy Lync Phone Edition devices, which are stand-alone IP phone devices provided by Microsoft partners.

Users can have multiple phone devices registered with Lync Server 2010, and can switch between them easily.

Users are alerted to incoming calls on all their devices simultaneously, with customizable ringtones on IP phone devices and a notification similar to an instant message on their PC.

Users can also set a single telephone number that connects to their desk phone, PC and mobile phone, so they can be reached no matter where they are.

While on a call, a user can answer additional incoming calls or initiate outgoing calls, and the existing active call is automatically put on hold. Calls can be transferred from one user to another, either directly or after the first user speaks privately with the second user. Users can also transfer calls to another device; for example, they could transfer an active call to their mobile phone as they walk out the door of their office.

When talking to another user with Lync 2010, users can easily add text, video, or desktop sharing to the call. The Do-Not-Disturb feature is integrated with the presence settings in Lync 2010.

With Unified Messaging, Lync 2010 and Lync Server 2010 integrate with Microsoft Exchange Server 2010 and Microsoft Outlook 2010. Users can see if they have new voice mail both in their Lync 2010 window and in email. While in email they can click to play the voice mail audio in an email message, or view a transcript of the voice mail message.

Enterprise Voice includes several advanced calling features as well, such as delegation, team calling, and Response Groups.

Delegation enables users to delegate call handling to one or more assistants. The delegate can perform multiple calling tasks on behalf of the user, including screening calls, placing calls, and initiating conferences.

Team calling enables a user to have incoming calls simultaneously ring the phones of teammates, for functions such as group call pickup and department calling.

Response Groups can be set up for queuing and intelligently routing calls to designated agents. Common uses include IT helpdesks, human resources hotlines, and other internal contact centers.

Lync Server 2010 uses standards and published interfaces to interoperate with existing infrastructure. It supports both gateway and SIP options (such as SIP trunking) for interconnection to IP PBX systems and the PSTN networks, so that you can migrate users to Enterprise Voice over time, while minimizing disruption. Lync Server supports traditional codecs such as G.711, G.722, and G.723.1 for interoperability with traditional VoIP solutions.

With call admission control (CAC), administrators can set limits on the amount of Lync Server voice and video traffic carried on constrained network links, and specify the action to be taken if a new call would exceed the limit. The actions could include routing by an alternate path, or refusing the call.

Lync Server 2010 works with third-party Survivable Branch Appliances to provide local calling services and connection to PSTN at branch offices, in case of WAN or failure at the central site.