I am new to iphone/itouch development and I am wondering if everyone keeps an inventory of all the hardware models (iphone 2G, 3G, 3GS, iTouch 1st Gen,2nd Gen etc.) in-house for testing purposes? Or is it reasonable to just test on whatever you have and solicit beta testers from the public? Ideally it makes sense to test on all the models, but since the iphone/itouch is a fairly closed system (unlike Android for example), there really isn't a big difference between say for example iphone 2G and 3G to require keeping both (or is there?)