You've probably hit a wall of frustration when you've tried to avoid outrageous charges for long-distance calls made from pay phones.

Changing Times, The Kiplinger Magazine, has advised consumers to avoid alternative-operator services by using five-digit access codes to reach major long-distance carriers. Alternative-operator services sometimes charge up to six times the standard rate for calling-card and other operator-assisted pay-phone calls.But if you try to use those codes (10288 for AT&T, 10222 for MCI and 10333 for US Sprint), you probably won't get through. Many private pay-phone owners block the codes. They say callers have found ways to use the codes to bill calls to the pay phone instead of to their home phone. Some proprietors have also blocked long-distance carriers' 800- and 950- access numbers, but a law that went into effect in January banned that practice.

The new law does not prohibit blocking the five-digit codes, and that's the only way to reach AT&T from a pay phone (other than by asking a competitor's operator to connect you). Within the year, the Federal Communications Commission must review the problem and decide whether to ban blocking entirely or to require AT&T to set up another way for pay-phone callers to get through.

Meantime, if you get stuck with an outrageous phone bill for a long distance pay-phone call, complain to the FCC's Enforcement Division (Common Carrier Bureau, 2025 M St., N.W., Suite 6202, Washington, DC 20554). In most cases, says FCC attorney Kurt Schroeder, the operator service will agree to refund the difference between what you paid and what your long-distance company would have charged.