Here is Link to the article provides step-by-step troubleshooting for Microsoft Lync Server 2010 connectivity issues for external users with mobile devices.

Lync mobility is the latest offering from the Microsoft Lync Server team.

http://blogs.technet.com/b/nexthop/archive/2012/02/21/troubleshooting-external-lync-mobility-connectivity-issues-step-by-step.aspx