(Updated (4/11): Lync Mobile client for Android phones are released as well.
The Lync Team just released the new Lync 2013 Mobile clients for Windows Phone and iPhone and iPad. This is exciting since the new releases enables audio and video calls from the mobile device. Take a look at the following post for a complete update of the feature enhancements:
Please note that your account will need to be on a Lync 2013 with Cumulative Update 1 loaded (http://www.microsoft.com/en-us/download/details.aspx?id=36820).
Here is the specific link for:
Lync 2013 Mobile App for Windows Phone
Microsoft Lync 2013 for iPhone by Microsoft Corporation
Microsoft Lync 2013 for iPad by Microsoft Corporation
Microsoft Lync 2013 for Android by Microsoft Corporation