The market for handheld computers may be staging a comeback, thanks in large part to Research In Motion ( RIMM), according to data released today by Gartner. Handheld makers shipped 2.75 million personal digital assistants (PDAs) in the second quarter, up 12% from the same period a year ago, according to Gartner. Research In Motion's shipments grew 289% to 510,000 units, making it the third-largest handheld maker in terms of volume. In terms of units, RIM's shipments increased by nearly 380,000 -- or about 1.3 times the total amount by which overall handheld shipments increased. Gartner attributed RIM's success to growing business demand for handhelds. "The second-quarter results show a continuing shift from what has been a predominantly consumer market to a market in which more than one-third of all PDA purchases are made by organizations," said Gartner analyst Todd Kort in a statement. Hewlett-Packard ( HPQ) and Dell ( DELL) also gained share in the quarter, according to Gartner. H-P, the No. 2 handheld maker in terms of volume, shipped 529,773 units in the quarter, up 38.9% from the second quarter last year. Meanwhile, Dell shipped 147,500 handhelds, up 6.5%. H-P's market share was 19.3% in the quarter, while Dell's was 5.4%. Market share losers included PalmOne ( PLMO) and Sony ( SNE), according to Gartner. PalmOne's shipments declined 3.2% to 913,202, giving it a 33.2% share of the market. Sony, which announced last month that it was exiting the PDA market, saw its shipments decline 35.9% to 174,804 units. The consumer electronics giant held a market share of 6.4% in the quarter, good enough for fourth place. Gartner's data stands in contrast to research released earlier this week by IDC. IDC reported that handheld shipments declined 2.2% in the second quarter from the same period last year to 2.2 million units worldwide.