How about having communications hardware that provides IP telephony even in case of WAN outages?

As one of the first solutions OfficeMaster SBA supports the Microsoft Lync Server 2010 and ensures that phones keep operating in branch offices even if the wide area network (WAN) fails. Until now, many companies have preferred to separate their IT and their telecommunications to prevent telephony being affected should the network go down. The OfficeMaster SBA switches over to ISDN if the IP connection to headquarters is interrupted, thus retaining all telephony functions.

OfficeMaster SBA is from Microsoft qualified as Survivable Branch Appliance for Lync Server 2010 and 2013

Data sheet OfficeMaster Survivable Branch Appliance
Data sheet OfficeMaster Gate UC

Lync Partner Solution Brief OfficeMaster SBA
Case study MedcoEnergi - Energy Company Reduces Costs by Upgrading Communications Solution