For organizations like ours that have Smart Card login enforced (no user/password), we are unable to use iOS, Windows Phone and other clients except Lync "desktop" Client from domain joined computer (user is logged on to computer with SmartCard therefore it has kerberos ticket issued). If Lync non-desktop client could support client certificates, we could easily export client cert from smart card and import it to iOS, Android and Windows Phone devices. This is a great show stopper for broader usage and popularization of Lync deployment.
Idea No. 328