The high court voted 6-3, with Justices William J. Brennan, Thurgood Marshall and John Paul Stevens dissenting, that the law can prohibit obscene messages, which are not protected by the First Amendment guarantee of free speech.
But there was unanimous agreement that the First Amendment does not permit a ban on all indecent dial-a-porn messages.
Neither the 1988 law nor the court yesterday spelled out the difference between "obscene" and "indecent" communications.
Under an earlier Supreme Court definition, speech is obscene if, applying contemporary community standards, it appeals to "prurient interest," contains "patently offensive" sexual conduct, and has "no serious literary, artistic, political or scientific value."
In a 1978 case, the court said, "The normal definition of 'indecent' merely refers to nonconformance with accepted standards of morality."
Harvard constitutional scholar Laurence Tribe said that "indecent" speech is "vastly broader" than "obscene" expression. "The language of indecent speech might be merely suggestive, not necessarily sexually explicit, like passages in racy, romantic novels or R-rated movies," he said.
Tribe, who argued the Supreme Court case on behalf of Sable Communications of California Inc., a dial-a-porn company, said he found it "encouraging and important that all nine justices say that parents should be relied on to take care of their children rather than to have government play Big Brother."
But the court ruling infuriated many conservatives, such as Rep. Thomas J. Briley (R., Va.), who co-authored the dial-a-porn ban with Sen. Jesse Helms (R., N.C).
"I'm not surprised that the same court that has ruled it legal to desecrate the United States flag would also allow indecency to be transmitted over the telephone," Briley said.
"The Supreme Court might think such indecent sexual messages are protected by the First Amendment, but I guarantee that every parent in this country does not."
The justices said Congress has the legal authority to protect children from dial-a-porn, which has ranged in degrees of offensiveness from sophomoric sexual puns and salacious groans to graphic descriptions of a woman having sex with a dog.
Congress made several unsuccessful efforts to solve the problem, finally concluding that only a total ban would protect children adequately.
The law made it a crime to use a telephone to make any "obscene or indecent" communication for commercial purposes. The total ban was never imposed, however, because U.S. District Judge A. Wallace Tashima in Los Angeles ruled it could be applied only to obscene messages.
White said Congress enacted the 1988 ban without evidence that less drastic measures would not work. In fact, Congress heard testimony that an untried Federal Communications Commission plan to require a system of access codes, credit cards and signal-scrambling devices would prevent nearly all children
from dialing the pornography numbers.
White said that if the FCC's technological approach to restricting dial-a- porn messages were adopted, "only a few of the most enterprising and disobedient young people will manage to secure access to such messages."
As White observed, "Dial-a-porn is big business." In New York City alone, one firm received six million calls a month in early 1985. Callers are billed for the service, usually by a charge added to their telephone bills.
Justice Department lawyers, defending the ban, said the messages are psychologically harmful to children and easily available "at the touch of a few buttons at home, at a friend's house or at any public phone booth."
Yesterday's rulings involved two cases, Sable Communications v. FCC and FCC v. Sable Communications.