HELSINKI (Reuters) - The world's top cellphone maker Nokia said on Monday it would start to make small laptops, netbooks, entering a fiercely competitive, but fast growing market. The first netbook, Nokia Booklet 3G, will use Microsoft's Windows software and Intel's Atom processor -- offering up to 12 hours of battery life, and weighing 1.25 kilograms, Nokia said in a statement. Nokia said it would unveil detailed specifications, market availability and pricing on Sept 2.