The phones may be wireless, but that doesn’t mean there aren’t strings attached. Here are 10 all-too-common ones and how to deal with them.

Carriers often charge differently for data than for voice transmission. And “data,” by their definition, can include text messaging, e-mail, photos, music, or Internet pages.

CR’s advice: If you expect to use your phone heavily for anything besides talking, ask your carrier about the cost of adding a data plan to your contract.

This can happen not only when you switch plans but if you change numbers, add features, or simply get a new cell phone.

CR’s advice: Never switch anything without asking the carrier whether there’s a catch. Chances are, there is.

When you download special features, such as a ring tone, game, or wallpaper, you may find yourself enrolled in a monthly plan.

CR’s advice: Look for any check boxes when you download a feature online, and be sure to uncheck them if they’re committing you to ongoing service you don’t want. Also read the terms carefully. Be especially wary when downloading anything from third parties.

The prices you see in TV and print ads don’t include all the taxes, surcharges, and fees that the provider will likely pile on.

CR’s advice: Expect to pay up to 30 percent more than the advertised price and compare plans on that basis. Before you commit, have the carrier list all the extra charges and explain how they will be calculated.

Judging by our survey, that seems to be a particular problem for people who buy phones from independent Web sites. In June 2006, the Washington, D.C., attorney general sued InPhonic, which operates sites including Wirefly.com, alleging that it “imposes restrictive conditions on the rebates that prevent many consumers from receiving the promised savings.” In a letter on its site, InPhonic says it “respectfully disagree[s]” that its practices are too restrictive.

CR’s advice: Buy from a retailer that gives the full discount up front.

Just because monthly minutes roll over doesn’t mean they never expire. For example, Cingular’s rollover minutes expire 12 months after they’re accumulated. You might also lose your rollover minutes when you switch to another plan, such as from an individual to a family one.

CR’s advice: Know how your rollover minutes are handled, and use them before they do their vanishing act. If you also have landline long-distance service, make those calls on your cell instead if you’d otherwise lose the minutes.

Most of Europe and much of the rest of the world is on GSM networks, the type used by Cingular and T-Mobile. But even if you have a GSM phone, it might not work overseas unless it’s using the proper band. What’s more, if your phone does work and you haven’t made arrangements with your carrier for international calling, you could end up paying astronomical prices.

CR’s advice: Ask your carrier whether your phone will work in the areas you’ll be visiting and, if so, to turn on international roaming. If not, your carrier might be able to rent you another phone.

Family plans often seem like a good deal, both for convenience and for cost. But you’re likely to face separate activation and termination fees for each family member’s phone, and you may have a hard time controlling your kids’ calls.

CR’s advice: Consider putting children on a prepaid plan, which limits available minutes to the number you’ve purchased. That will not only control costs but may even teach your kids to be responsible with their airtime (although we’re not making any promises).

If you cancel during the trial period (usually 15 to 30 days), you shouldn’t have to pay an early-termination fee, but you’ll still be on the hook for such things as activation fees, access charges, equipment-restocking fees, taxes, and airtime.

CR’s advice: Don’t rely on the trial period as a way to choose carriers but only as an opportunity to bail out if you’ve made a bad mistake. Instead, consult our Ratings on page 29. Also ask neighbors how they like their carriers.

Carriers will do almost anything to keep you in their contractual grip, whether that’s offering discounted or free phones with the latest technology or giving you additional airtime for the same price.

CR’s advice: Don’t be pressured. Usually you can just continue with your current plan on a month-to-month basis, which gives you the freedom to switch carriers or upgrade equipment whenever you decide to. If you do decide to renew, don’t hesitate to try negotiating for better terms. This might be the only point in the process when you, not the provider, hold the upper hand. Enjoy it.