Masab Yousef, son of West Bank Hamas leader Sheikh Hassan Yousef, has become a Christian (already a number of years ago). Recently, he has made his testimony public.
His written testimony (in form of an interview) is available here: Prodigal Son (1 August 2008)
A Fox News interview: Son of Hamas Leader Turns Back on Islam and Embraces Christianity (text and video, 12 August 2008)
Escape from Hamas (6 part YouToube series of a TV interview on Fox News, January 2009)
Answering Islam Home Page