Microsoft had just released a public hot fix to remediate issues on iPad 2 running on iOS 7.1 where the Lync Client is unable to place or receive Audio & Video Calls

The Lync 2013 for iPad client cannot place or receive audio or video calls when the client is hosted on iPad 2 devices that are running iOS 7.1

The symptom doesn’t happen on Lync Client running on iPad Mini or the iPad Air, running on iOS 7.1

Kudos to the Lync Engineering team is identifying and resolving this matter!