If there are openings, the adcom will usually begin making phone calls middle of May and continue until the number of empty spots are filled. Usually in June/July, a final notification letter will be sent if no more applicants will be called from the WL. Best of luck to you (and hope you are content with where you've been accepted).
Replies to: Waitlist
This article may be of interest to you.
College wait lists prolong the angst for high school seniors - Philly.com
Haverford
2012 . . . 3
2011 . . . 0
2010 . . . 1
2009 . . . 13
2008 . . . 3