Screenshot swiped from Matt Landis at http://windowspbx.blogspot.com/2011/12/first-impression-review-of-lync-mobile.html
Once you get Lync Mobile going, you pretty much never need to sign in (if you’ve selected “remember my password” on the login screen). But there might be times when you really do want to sign out – most likely for troubleshooting. I found the Sign Out seeting in a semi-logical place. It’s in the area where you can set your status.
The screen shot shows where you need to look.
Right there at the very bottom is the “sign out” option.