Just a fyi if you plan to engrave something on the back of the iPhone. It's plastic cover, not metal. So tell the shop to level down the laser power before it penetrates the back.
http://chinese.engadget.com/2007/07/20/laser-etching-the-iphone/
http://chinese.engadget.com/2007/07/20/laser-etching-the-iphone/