My sister dropped her iPhone 4 and shattered the screen. Luckily she had already ordered a new front and back to change the color but we couldn't get the first 2 screws out because they weren't philips head.
I had already replaced my screen and back so it went very smoothly. Took about 40-45 minutes.
Be careful when changing the button, its glued to a thin wire that tears easily and will break your home button completely if ripped. If you do break it, there is a setting to give a Home button on your touch screen display which is annoying but works fine until you can get a replacement button.