Apple on Friday began selling the high-speed wireless version of the iPad in the United States, following the launch of the Wi-Fi tablet earlier this month.

The new 3G model is also Wi-Fi compatible. It starts at $629 and tops out at $829. The Wi-Fi-only iPad starts at $499.

The 9.7-inch touchscreen iPad is essentially a cross between a laptop and a smartphone. The device allows users to browse the web, read and send email, enjoy and share photos, watch HD videos, listen to music, play games, read ebooks and much more, all using iPad's Multi-Touch user interface. iPad and deliver up to 10 hours of battery life for surfing the web on Wi-Fi, watching videos or listening to music, and up to nine hours of surfing the web using a 3G data network.

AT&T is providing the wireless data plans for the iPad, charging $15 for 250MB per month or $30 for unlimited data.

Apple said that it sold its one millionth iPad on Friday, just 28 days after its introduction on April 3. iPad users have already downloaded over 12 million apps from the App Store and over 1.5 million ebooks from the new iBookstore. Although the device won't reach international markets until late May, some analysts expect Apple to sell roughly 5 million or so this year.