I've found an issue where Lync 2013 SBA users could not use mobility due to the undocumented UCWA port, TCP 5088, being filtered by a firewall. The Lync 2013 mobile client would sign in but would time-out during any attempt to use IM.
Please refer to my buddy, flinchböt, who wrote the findings and solution on his blog, http://flinchbot.wordpress.com/2014/07/01/port-5088-missing-from-lync-2013-documentation/
