I created this simple screen to help me debug mobile UI. It's just a simple iframe with html. Unless you have multiple handheld devices available in your lab, I hope you will find this helpful too. For a 'real' mobile browser in desktop browser, I recommend Opera mobile.

If there's an additional screen res. you want to see being included here, or any other enhancement in mobile usability/accessiblity testing, please don't hesitate to drop me a mail.