The size medium Timbuk2 case is a perfect fit for average-sized smartphones like a Motorola Droid or Apple iPhone, either with or without a slim skin case. Don't know how well it will work some of the new super-sized Android phones. Unlike a lot of cases, this one is thin and not bulky, but still has a thin fleece inner surface to protect your touch screen. The Velcro on the back is designed to wrap around a vertical strap like on a messenger bag or backpack. Won't work so well on a horizontal belt. Note that the case is not waterproof since there are holes on the sides.