Global smartphone shipments surged 55 per cent in the fourth quarter, as demand for Apple\'s iPhone 4S countered declines by Research In Motion and Nokia Oyj, International Data Corporation said.Shipments advanced to 158 million units from 102 million a year earlier, exceeding IDC\'s forecast for a gain of 40 per cent.Smartphone demand is increasing as prices for devices become more affordable, encouraging users to upgrade to handsets on which they can browse the web and send email.Existing users are also trading up to more powerful smartphones such as the iPhone 4S, which went on sale in October. Apple sold 37 million iPhones last quarter, helping the company to double its profit in the period.By the end of 2011, one out of every three mobile phones shipped worldwide was a smartphone, and the iPhone 4S \"played a key role in smartphone growth to capture pent-up demand\", said Ramon Llamas, an analyst at IDC.Apple\'s share of the global smartphone market jumped to 24 per cent from 16 per cent a year earlier, regaining its top spot from Samsung, which had overtaken the iPhone-maker in the third quarter.Samsung\'s share climbed to 23 per cent in the fourth quarter from 9.4 per cent a year earlier, IDC said.Nokia and RIM, both of which are struggling to reverse slumping sales with new phone operating systems, saw their respective share shrink.Nokia\'s share fell by more than half to 12 per cent from 28 per cent a year earlier, and RIM\'s dropped to 8.2 per cent from 14 per cent.