NEW YORK — Apple Inc.'s iPhone, a new model of which is widely expected this summer, took 19.2 percent of the U.S. market for "smart" phones in the first quarter of 2008, according to research firm IDC's vendor survey.

That was down from 26.7 percent of smart phones sold in the fourth quarter of last year, which included the holiday shopping season, IDC found.

Much of the slack was picked up by Research In Motion Ltd.'s BlackBerry, which took 35.1 percent of the market in the fourth quarter and then 44.5 percent in the first.

IDC analyst Ramon Llamas said the BlackBerry is now strong in the "prosumer" segment, as RIM has successfully widened the appeal of the device beyond the professionals who have been its core customer group.

Smart phones are designed for Web surfing and e-mail in addition to voice calls and usually have alphabetic keyboards or touch screens. They account for a growing share of cell phones sold, as prices descend and carriers complete their fast data networks.

IDC did not reveal the total number of smart phones sold in the quarter. Apple said it sold 1.7 million iPhones in the first quarter, including overseas sales.

Palm Inc., a pioneer in the category along with RIM, also picked up market share in the first quarter, when it grabbed 13.4 percent of smart phone sales, up from 7.9 percent in the fourth quarter, IDC said.

But Palm's market share is down from 23 percent in the first quarter a year ago, apparently the victim of the iPhone, which went on sale late last June. RIM's market share is also down from last year, when it sold 48.7 percent of U.S. smart phones in the first quarter.

No. 4 in market share in the most recent quarter was Samsung Electronics, with 8.6 percent, up from 5.1 percent in the fourth quarter, a rise Llamas credited to the availability of the BlackJack on Verizon Wireless.

Motorola Corp., which is struggling in the overall cell-phone market, did poorly in smart phones as well, dropping from a 7.5 percent share in the fourth quarter to 2.6 percent in the first.