By Sakari Suoninen and Jussi Rosendahl HELSINKI (Reuters) – Nokia surprised investors with strong quarterly earnings and raised its full-year profit margin forecast as network operators install more powerful systems to cope with surging mobile data traffic. The Finnish company sold its once-dominant phone business to Microsoft in April, leaving it more reliant on a mobile network equipment business that shrank by 8 percent in the April-to-June quarter. Much of the decline was due to foreign currency fluctuations and divestments and Nokia said it expected network sales to return to growth in the second half of the year after a period in which the company sought to exit unprofitable contracts. The company raised its profitability estimate for networks, saying its operating margin this year would be at or slightly above the high end of a long-term target of 5 to 10 percent.