A: Microsoft released the Lync client for Windows Phone 7.5 to Windows Phone Marketplace in December 2011. The easiest way to get the application is to just go to Marketplace on your phone and search for Lync.
The other option is to install it from the web by navigating to the Lync 2010 webpage for Windows Phone and selecting the Install option.
Still got issues? Check out all of the FAQs for Windows by John Savill.