In addition to "plain old telephone service," you can buy extra services such as voice mail, paging, and Internet access from many different companies. But when charges show up on your phone bill for services you never agree to buy, you've been "crammed."

• Be aware that charges for many types of services can appear on your phone bill. In addition to billing for its own services, your phone company may bill you on behalf of other companies for services they sell such as voice mail, paging, or Internet access—even for club memberships and other types of services. Cramming is when a company charges you through your telephone bill for extra services that you never agreed to buy.
• Read the fine print. Contest entry forms, product coupons, checks and other promotional materials could include an agreement to buy a service that will be charged to your phone number.
• Beware of imposters. Someone posing as a representative from your phone company may try to trick you by asking about your satisfaction with your service or telling you about a service change. A “yes” answer to a question could be tape-recorded and used as proof that you agreed to buy a new service. Ask for the caller’s name and number, and contact your phone company to find out if the call was legitimate.
• Look at “junk mail” carefully. It could be a “negative option” notice that you will be charged for a service unless you contact the company to cancel it.
• Be careful about returning calls to numbers on your Caller ID that you don’t recognize. A crammer may use Automatic Number Identification to see the number you’re dialing from and process an unauthorized request for service.
• Check your phone bill carefully. If you are unsure about charges that appear on your bill, call the number listed on that page for billing questions and ask for an explanation. Keep on checking, because even if the charges are removed one month, they may pop up again the next month.
• You aren’t responsible for charges you never authorized. But it’s important to notify your local phone company about the problem and pay the rest of the bill on time.
• Ask your local telephone company about “bill blocking.” There may be a way to prevent someone from putting charges for extra services on your phone bill unless you have confirmed directly with the phone company that you agreed to purchase them.