Most cell-phone companies don’t offer the type of detailed coverage maps now available from Cingular and T-Mobile. That means consumers need to do more footwork when picking a carrier.

The stakes are higher than you might think when buying a $40-a-month plan.

Carriers generally require customers to sign a one- or two-year service contract, so a $40 plan means a commitment to spend at least $500 or $1,000 after taxes and other fees. If they want to get out of that agreement, customers must pay termination fees averaging about $175 per line. On top of that, some cell-phone stores charge an additional cancellation fee – as much as an additional $300 per line.

To avoid being surprised by such fees, make sure you read all the terms of any contracts you agree to follow. If you’re buying from an agent and you’re asked to sign two sets of documents, you need to read the terms of both agreements.

If you don’t understand what you’re signing, hold off on getting the phone.

Take a copy of the contracts with you and get somebody to go over their terms with you.

Here are some other things to consider when buying a phone: When you’ve decided what features you want in a phone, and how many minutes you need in a plan, visit a cell-phone store and price a handset that meets your needs. Take good notes.

Check prices of all phones and calling plans that you’re considering. Find out what “extras” are included in each offer – many include rebates and “free” accessories. The best place to do this is the Web, where there’s no pressure from salespeople, many of whom work on commission.

Most cell-phone companies give customers about two weeks to return a phone with no penalty. Use that window to make sure you’re satisfied with your new service. Try it out everywhere you expect to use it regularly. If you’re not completely happy, return it immediately along with the receipt, accessories and original box.

Remember that you can get a “prepaid” phone without signing any contract.

This often makes sense for people who don’t use cell phones often, but want one for emergencies. TracFone, the biggest prepaid carrier in the United States, sells phones that operate on the Verizon network as well as those that work with the Cingular/T-Mobile Network. Virgin Mobile phones use the Sprint network; Boost Mobile’s handsets work on Nextel’s network.

If you are switching carriers and want to keep your current phone number, take a phone bill with you when you order the new service. That way the agent will be able to enter your information exactly as it’s stored in your current provider’s computer system, reducing the potential for glitches.

Here are five rules to follow to make cell-phone shopping more rewarding:

1. Ask friends, family and co-workers how their cell phones work in the areas where you live, work and visit. Use this information to narrow your choice.

2. Estimate “anytime” minutes you’ll use each month. (One rule of thumb – make a generous forecast of how many minutes you’ll be on the phone on a typical weekday, then multiply by 20.) Because many plans offer free calls on nights and weekends, you’ll generally use “anytime” minutes for 7 a.m.-7 p.m., Monday to Friday, but that can vary by carrier and even plan.

3. List the features you want in your phone. Are you a meat-and-potatoes user who just wants a phone that works? Or are you a gadget lover in search of an electronic Swiss Army knife with a phone, camera, PDA and Web browser?

4. Comparison-shop online and in stores.

5. Read the contract and understand its terms before you sign on the dotted line.