WASHINGTON — Sen. Barack Obama's pledge to supporters that they would be the "first to know" his running mate turned out to be a savvy but unworkable communications strategy.

The Democratic presidential candidate got scooped by the media on his own announcement, done in by dogged reporting, loose-lipped party insiders and the limits of technology.

But all was not lost. He amassed a huge database of cell phone numbers and e-mail addresses for the fall campaign.

Obama's plan to use text messaging to announce his choice was a first in politics. He had promised supporters that by providing cell phone numbers and e-mail addresses they would be "part of this important moment" — the declaration of his choice for vice president.

The text message announcing Biden as Obama's pick began filtering across the U.S. early Saturday, when most people were asleep. By then, it was old news, by today's standards. The media had reported the pick more than two hours earlier.

Michael Silberman, a partner at online communications firm EchoDitto, said the campaign gambled when they made such a high-stakes promise and find themselves in a precarious situation where they could risk a great deal of trust with supporters.

"For Obama supporters, this is like finding out from your neighbor instead of your sister that she's engaged — not how you want or expect the news to be delivered," Silberman said.

The campaign won't say how many people signed up to receive the text message, nor will the small Washington, D.C., company that handled the imposing chore.

"It's a big number," said Kevin Bertram, the 37-year-old founder and CEO of Distributive Networks.

The 16-employee firm, which built the text messaging system, has higher-paying clients. According to Federal Election Commission records, it has received about $130,000 from the Obama campaign, not including August.

But no account has a higher profile, Bertram said.

"We have seen some text campaigns in the many hundreds of thousands of opt-in mobile users over the past couple years, all in the consumer products-services realm," said Verizon Wireless spokesman Jeffrey Nelson. "This is the first massive effort in the political world."

He said the scale appeared similar to Olympics updates, which occur several times a day.

CTIA, the wireless industry's lobbying organization, says in the month of December alone, there were more than 48 billion text messages sent in the U.S.

The real test for Distributive Networks was speed.

"It's a pretty big challenge, because we're under a strict time constraint to get all those messages out," Bertram said.