www.networkworld.com/news/2011/012011-the-case-of-apples-mystery.html, posted 2011 by peter in apple business crapification hardware
If you want to remove the outer casing on your iPhone 4 to replace the battery or a broken screen, it won't be easy anymore. In the past, you could use a Phillip screwdriver to remove two tiny screws at the base of the phone and then simply slide off the back cover.
But Apple is replacing the outer screw with a mysterious tamper-resistant screw across its most popular product lines, reports iFixit, a Web site that provides free repair manuals and advice forums mostly aimed at Apple products. Apple calls them "Pentalobular" screws.
New MacBook Pros, iPhone 4s and MacBook Airs will have the Pentalobular screw, making it harder for do-it-yourselfers to make repairs. What about existing products in the field? Pentalobular screws might find their way into them, too.