Nearly 6 million mininotebooks, or netbooks, were shipped in the first quarter of 2009, raising their standing within the notebook PC market to almost 20 percent, market forecaster DisplaySearch is reporting.

Netbook penetration in North America, China and Japan was lower than in Europe, the Middle East and Africa, which DisplaySearch wrote may be attributed to telecommunications subsidy plans in Europe that combine discounted netbooks with carrier subscriber plans.

(U.S. carriers have taken note, and AT&T recently announced a trial plan in Atlanta and Philadelphia, offering a choice of netbooks with starting prices as low as $49.99 for new subscribers to its Internet at Home and On the Go home and mobile broadband service.)

While Hewlett-Packard saw the highest total notebook PC numbers in the industry, shipping 7.3 million total units in the first quarter of 2009, Acer, which recently scaled back its netbook shipment forecasts, shipped the most netbooks—1.8 million units to HP’s 700,000.

Acer also shipped more than Dell, boosting itself from the No. 3 notebook PC maker to No. 2. Netbooks and notebooks combined, Acer shipped 5.7 million units to Dell’s 4.3 million, 400,000 of which were netbooks.

In fourth position, Toshiba shipped 3 million total mobile units in the first quarter of 2009, of which 200,000 were netbooks. Fifth-place Lenovo shipped a total of 2.1 million units, which included 200,000 netbooks, and sixth-place Asustek Computer shipped 1.7 million units, 900,000 of them netbooks.

Asus is expected to release an 11-inch netbook later in May, and Lenovo and Dell recently announced netbook updates.