Having watched its shares lose nearly half of their value in the last year and its cell phone business continue to languish among the also-rans in a crowded field, Motorola will split into two publicly traded companies, separating its mobile devices business from its broadband and mobility solutions group. Motorola, whose Razr phone has been left behind by market-changing products from Nokia and Apple, has been trying to fend off pressures from outside and inside the company.