A spokesman for Verizon said the decision turned on the subject matter of the messages and not on Naral’s position on abortion. “Our internal policy is in fact neutral on the position,” said the spokesman, Jeffrey Nelson. “It is the topic itself” — abortion — “that has been on our list.”

Mr. Nelson suggested that Verizon may be rethinking its position. “As text messaging and multimedia services become more and more mainstream,” he said, “we are continuing to review our content standards.” The review will be made, he said, “with an eye toward making more information available across ideological and political views.”

Naral provided an example of a recent text message that it has sent to supporters: “End Bush’s global gag rule against birth control for world’s poorest women! Call Congress. (202) 224-3121. Thnx! Naral Text4Choice.”

Messages urging political action are generally thought to be at the heart of what the First Amendment protects. But the First Amendment limits government power, not that of private companies like Verizon.

In rejecting the Naral program, Verizon appeared to be acting against its economic interests. It would have received a small fee to set up the program and additional fees for messages sent and received.

Text messaging programs based on five- and six-digit short codes are a popular way to receive updates on news, sports, weather and entertainment. Several of the leading Democratic presidential candidates have used them, as have the Republican National Committee, Save Darfur and Amnesty International.

Most of the candidates and advocacy groups that use text message programs are liberal, which may reflect the demographics of the technology’s users and developers. A spokeswoman for the National Right to Life Committee, which is in some ways Naral’s anti-abortion counterpart, said, for instance, that it has not dabbled in text messaging.