It seems that Apple have introduced a new type of screw head into the casing of the iPhone 4.
The “pentalobe” presents an entirely new interface to your tollkit, and is not compatible with hex heads, or torx, or phillips heads, or ….
And no, you can’t buy tools that undo them yet either; not easily, at any rate.
The latest MacBook Air systems are also using these new screws, making it very difficult for you to even install more storage, should you wish to.