(MONEY Magazine) – What's the biggest phone gripe these days? It's not slamming (finding your long-distance service switched without permission). It's "cramming," a rapidly growing phenomenon in which charges for unwanted services, such as call waiting or paging, show up on your bill--at up to $40 a pop. The 2,000-plus cramming complaints lodged in the first half of the year outnumber those for slamming by two to one.

Either your local phone company or an outside firm may charge you for services you didn't order--or get. In July, at the urging of the Federal Communications Commission, phone companies adopted anti-cramming guidelines, which should be in effect everywhere by early next year. They include verifying requests for new services and naming on your bill the firms that are charging for them. Plus, the Federal Trade Commission (FTC) vowed to crack down on the firms that sell or collect fees for bogus services.

How do you spot cramming? "Many billers give legitimate-sounding names to these charges," warns Teresa Schwartz, deputy director of the FTC's Bureau of Consumer Protection. Items such as "Miscellaneous Charges and Credits," "Minimum Usage Fees," "Activation," "Call Manager," "Basic Access," "Special Plan" or "Enhanced Services" could be real charges--or evidence of cramming.

If you think you've been crammed, call the 800 number on your bill and ask that the suspicious charges be verified or removed. You should still pay the other items on your bill. Follow up with a certified letter, and get in touch with the FTC (202-326-3134; www.ftc.gov).

--BRIAN L. CLARK