This may seem silly to some, but to iPhone distributors outside the US using carriers other than Sprint, At&t and Verizon it may be a little confusing... (some grandmothers and parents might find it useful for buying presents as well)
The first and perhaps most notable difference are the dividers on the side, the At&t phone only has one on each side. The second is the placement of the mute toggle and volume buttons. There is one other difference that doesn't not effect our skins. The Verizon iPhone 4 has NO sim card tray, our skins ALL have a sim card cutout, you can always leave that part in place while applying the skin.