Choosing the right 3G cell data plan is all about three things: coverage area, cost, and connection type.

Coverage: Where can you use it?

The single biggest factor in choosing a 2.5 or 3G network for cell data access is probably coverage. How well does the coverage area coincide with your home and travels? You?ll find links to the coverage maps offered by the networks in our chart of cell data plans. Think about where you?ll be when you need access: if you spend a lot of time in one area, you'll want to go with a plan that covers that region well without paying roaming charges. For instance, if you live in Alaska, you might want to go with ACS Wireless, which has better local EV-DO coverage than the national carriers. Alltel is another smaller carrier that offers EV-DO service in many areas not covered by the big networks, principally in mid-America. And SunCom offers EDGE service in its local areas, plus roaming to Cingular elsewhere.

If you spend a lot of time jetting around the country, also look at how well the different companies cover the airports and cities you travel to. Verizon and Sprint have focused their EV-DO efforts on big cities and travel hubs, and you can often get speeds up to 1.3Mbps.

A little time spent studying the maps can pay off in the long run by matching you with a network that works where you want to be. But take them with a grain of salt: many show a nation awash with coverage, but most of that may be lower-speed service. The cell phone companies don?t add a new standard or enhancement to their entire networks at once: they typically pick the most highly populated or strategically important locations to upgrade first. Outside of 3G areas, you'll likely see service step down to the 144Kbps 1xRTT or EDGE standards, which may not be acceptable for your needs.

Most of the networks offer the ability to check coverage by zip code, but some (such as Sprint) even show exactly where their cell towers are for an even better idea of how well an area will be covered.

T-Mobile has a page where you can check the actual signal strength you might get: its Personal Coverage Check site lets you enter an address and get a map of the anticipated coverage.

Cost: How much will you pay?

Most carriers offer unlimited high-speed data plans for $80 per month, or $60 with a voice plan, but both carriers and resellers aggressively compete on cell card prices, so it?s worth shopping around. You can get almost any card for less than $100 or even free with a little surfing. You'll almost always be stuck with a two-year contract, however.

Many companies also offer lower-priced plans that limit how much you can download, but these should be approached with caution. Much like voice plans, they are cheap up front, but they can quickly get WAY more expensive if you go over the limit. AT&T/Cingular, for example, offers a $20-per-month Laptop Connect plan that allows for 5MB of data transfers, with additional data costing .8 cents per KB. So if you go over the 5MB limit and then download a 10MB file, that'll cost you an extra $80! It's very easy to run over, especially if you are doing things like uploading photos, streaming audio, or using a VPN where you can't easily see how much data is being transferred. We only recommend unlimited data plans, although even those are not truly unlimited. Some carriers, especially Verizon, police your usage, and if you go over arbitrary limits, you may get cut off summarily. Sprint is known to be more generous in this regard.

Connection Type: How will you get online?

As mentioned earlier, there are two main ways to connect your laptop to a cell data network: via a cell data modem card that is built into your laptop or plugs into a PC Card or ExpressCard slot (which we recommend for more than occasional use), or through a data-capable cell phone tethered to your laptop via Bluetooth or USB. Carriers typically have one set of rate plans for PC Card users, and a separate set of voice/data plans for phone users (laptop tethering will usually cost extra). It pays to shop around, even within one carrier. See the hardware options page for more on cards vs. phones.

There are a couple other ways to use cell data, however. If you want the speed and reliability of a dedicated card, but don't have a slot, high-speed USB modem adapters are beginning to appear. And if you want to share your cell connection among multiple computers, several Wi-Fi routers are available that have built-in slots for your cell card. Two examples are the Kyocera KR1 Mobile Router and the Linksys Wireless-G Router for Mobile Broadband. These routers are particularly attractive for RVs, buses, trains and other situations where you can't use a wired Internet connection, but can even be placed in the home instead of a DSL or cable modem if you have good 3G cell reception in your area. Performance will be nowhere near DSL speeds, but still many times faster than dialup.