Mobile phone makers have taken such a beating lately that investors should be numb to bad news. They are not, and the latest warning from Sony Ericsson was grim enough to spark a sector rout. The world’s fourth-biggest handset maker by sales said it expected to ship just 14m phones in the first quarter – down 37 per cent from the year before. Shares in Ericsson, which owns 50 per cent of the company, plunged almost 9 per cent. Finnish rival Nokia fell more than 6 per cent. Suppliers suffered too. Infineon, one of the world’s biggest makers of the chips used in mobile phones, at one point fell more than 13 per cent.