Lync supports E911 so emergency responders can fix the location of callers using Lync. OCS did not support E911.

What is a Survivable Branch Appliance?

Lync Server 2010 has the capability to switch the WAN links used to carry communications among branches of a business. If the primary IP link fails, the Survivable Branch Appliance reconnects the branch with the outer world via the traditional public switched phone network. These gateways are made by third parties.

Is there support for legacy analog phones and fax machines?

Yes, Lync supports both, something OCS did not.