Clayton Miller's Interuserface takes a look at the iconic shapes behind today's biggest mobile companies, and while Apple, iPhone, and iPad are obviously roundrects (rounded rectangles), their competition is just as geometrically aligned:
Microsoft’s Metro UI owns the square. Apple has a corner on the roundrect, from the Springboard launcher to the iPhone hardware itself. Nokia, despite its late entry with MeeGo’s Harmattan UI, found the squircle unclaimed and ran with it beautifully. Palm has used the circle from the early days of PalmOS, and in WebOS, HP continues the tradition with care (one might even note that both Palm and HP structure their wordmarks around the circle).
Zune, obviously, couldn't hold the squircle, and neither Bada nor RIM could take the square or roundrect as their own. Interestingly, Google's Android has no iconic hold on any simple shape (nor do Facebook or Amazon for that matter, who have elected to stick with letters).