We all pack appropriate clothing when we leave for a business trip, but most mobile users will still feel naked if they don't have easy, fast access to the Internet.

Sure, you can stop at a Wi-Fi hot spot or catch up at the hotel at night, but what do you do the rest of the time? Enter cellular providers that offer 3G data service over their networks at broadband-like speeds.

Third-generation wireless technology, or 3G, started being rolled out in about 2001, and offers a wide range of services (from music downloads to mobile GPS) and greater efficiency than previous standards. In the U.S., three providers offer 3G service: AT&T, Verizon Wireless and Sprint. The fourth nationwide carrier, T-Mobile, says it will roll out its 3G network starting later this year.

Although 3G can be accessed using many cell phones, road warriors who need to get serious work done will likely want to use their laptops. To that end, more notebook makers are offering optional built-in cellular data network connections. For those of us who aren't ready to purchase a computer with that capability, there are numerous plug-in radio modems that can offer the connection.

To test these capabilities, I got hold of cellular network cards from AT&T, Sprint and Verizon, and used them with a Lenovo ThinkPad X300 notebook. I watched videos on commuter trains, worked with e-mail at cafes, listened to Internet radio at the airport and downloaded large files while in a car.

How we tested

To gauge the speed and reliability of these three wireless data networks, I used my ThinkPad X300 to collect nearly 500 data points at eight different places in New York, New Jersey and Connecticut, within a 50-mile radius of midtown Manhattan's urban canyons.

I timed how long it took to establish a connection with each network, followed by speed tests. Using Alken's bandwidth meter, I was able to gauge download and upload speeds as well as how long it took to load that vendor's home page. Finally, I ran an Internet radio station and timed how long it took to drain the battery. I then compared it to running the battery down using the notebook's Wi-Fi radio.

All speed readings -- connection time, the Alken speed tests and page loading times -- were repeated five times and averaged.

AT&T LaptopConnect

AT&T's LaptopConnect data network has definite appeal for those who live on the road. It not only delivered the fastest test speeds over its High-Speed Packet Access (HSPA) network, but AT&T gives you the card for free -- if you commit to a two-year contract.

The carrier offers the choice of four connection cards; I tested Sierra Wireless' USBConnect 881 USB card. The 881 card is tiltable, has a 380 milliamp/hour built-in battery and an external antenna jack (although AT&T doesn't sell an antenna for it). It weighs two ounces and slips easily into a notebook bag pocket, but when inserted in my test laptop, it blocked a nearby USB port.

The card automatically loads the needed software the first time you connect it to your laptop. AT&T's Connection Manager (ACM) software has an online timer, and shows the network's signal strength bars and how much data has moved into and out of the computer.

You also can use it to control the notebook's Wi-Fi connection, although its interface