If you are looking for the Official Microsoft Lync Mobile Client for iPhone and iPad it has been released Early 12/20/2012 (EST) For download links and my first Impression review:
Clarification: This article is not about the official Microsoft Lync Mobile client. Xync is a 3rd party client that is currently not a microsoft certified client. For more details on the the official Microsoft Lync Mobile client expected end of year 2011 see this URL:
Well it looks like Damaka will produce the client for Lync that Microsoft has not! And as a bonus it looks like audio and video will make it to the mobile as well. Damaka also notes that no extra server is required--this client registers directly to the Lync Server. (Like snom OCS edition apparently)
See video demo and more here:
PS- note that the vendor plans a WindowsPhone 7 "Mango" version of this software as well!
UPDATE: Android version has been released!
UPDATE: See my interview with maker of Xync on 9/19/2011 Here:http://windowspbx.blogspot.com/2011/09/interview-with-damaka-lync-for.html