If you’ve ever donated or sold one of your cell phones or smartphones, the TechNewsWorld article "Used Cell Phones May Reveal First Owners’ Personal Data" may make you gulp.
"Selling your old phone once you
upgrade to a fancier model can be like handing over your diaries. All
sorts of sensitive information pile up inside our cell phones, and
deleting it may be more difficult than you think."
Reference this useful article with links on Wiping Your Cellphone Clean of Personal Data for Blackberries, Treos and more.