Worldwide shipments of connected devices (tablets and smartphones) topped 1 billion in 2012 -- a 29.1% increase year over year, according to a press release published today by the International Data Corporation. 

Samsung remains the leader in smart-device unit-shipment market share, with 21.2%. But Apple (NASDAQ:AAPL) inched closer to Samsung with 20.3% in Q4 2012, because of iPhone 5 and iPad Mini shipments. Looking at the revenue share, though, Apple easily beats Samsung with 30.7%, compared with Samsung's 20.4%. 

Competition between the two companies is heating up, considering that the IDC expects tablet shipments to increase by 48.7% and smartphone shipments to increase 27.2% year over year in 2013. Keeping with the mobile trend, the research company expects tablet shipments to outpace desktop PC shipments this year and surpass portable PC shipments in 2014.

The IDC said that over the next four years, tablet shipments will grow by 174.5% and smartphone shipments will grow by 109.9%. The company also estimates that smart-device shipments will surpass 2.2 billion units in 2017, with revenues of $814.3 billion that year.