Mobile App with user tests

Working on a project which will result in a mobile app. The design process will involve a user test - i think 3 participants will be good number to test the design. Making productions work on different browsers and computers is a workload when working with the web. Creating design for mobiles is 300 times harder. Getting an application to work on Sony Ericssons, Nokias, iPhones, Samsungs, HTC's etc. is a real puzzle. It's a challenge and I really believe it will be smoother in years to come.