Pentalobe

iPhone 4

If you were hoping to buy a new iPhone 4 and tinker with it, you might have some problems.
Per the mighty iFixIt, Apple has begun replacing the standard phillips head screws that hold together most iPhones sold in the U.S. with tamper-resistant “pentalobe” screws. The result is a device that most users are unable to open which also proves difficult for third party battery replacement services to replaces the battery in the device.
The pentalobe screw is a design controlled by Apple, and getting a screwdriver is very difficult, unless you’re an Apple Certified repair technician. Apple is apparently replacing the old screws with the new ones whenever an iPhone is brought into an Apple Store for repair, and users aren’t alerted to the change before or after it takes place.
Pentalobe Screw from iFixIt’s explanatory video
The new screws have begun to surface in recently shipped iPhones and iPhone 4 models shipped with the screw in Japan from the get-go.
These same screws are used on some MacBook Pro and Air models, and are likely to make their way to more Apple products in the future.

Pentalobe