Good luck salvaging an iPhone screen. There's only one driver for that piece of hardware, and it's installed in the iPhone! For prototyping purposes, you should look at a piece of open-source hardware like Chumby, the OpenMoko Neo FreeRunner, etc. Good-quality touchscreens can be cheaply salvaged from old Palm devices, available in bulk on eBay. You should move this post to the correct competition to gain more accurate replies.
Project Manager/Designer - Team Stevens - Game Development<br>
Engineering Management Trainee, Stevens Institute of Technology