Motorola is building a family of cell phones based on the design and brand identity of its hot-selling Razr. The Krzr, one of several new models, is 12 millimeters narrower than the Razr, which is 54 millimeters wide. The Krzr, however, also is slightly thicker than the Razr to accommodate a 2-megapixel camera and storage space for 500 songs. The case is made of magnesium, polished chrome and hardened glass. The phone should be available worldwide by the end of the year.