"No other campaign has done this before," campaign manager David Plouffe said in the e-mail. "You can be part of this important moment."
The e-mail asks supporters to pass the message to friends and family, another way for the campaign to collect information on potential voters and contributors.
Obama has run a technologically savvy campaign, using the Internet to build a network of 2 million volunteers and raise nearly $340 million, as of the end of June.
The campaign's efforts extend far beyond the official campaign Web site, to a variety of social networking sites that allow supporters to exchange messages with each other, and track the candidate on the campaign trail.
Some of those sites, like Twitter, deliver updates via text message, putting the campaign in near-constant contact with potential voters.
Obama's latest Twitter update details the campaign's plan to announce a running mate via text.
That announcement could be the first high-profile step in an otherwise guarded process. Both Obama and likely Republican nominee John McCain have been tightlipped about who they're considering and how the process is going on.
Obama is vacationing in Hawaii with his family until Aug. 15. He'll return with just nine days to go before the Democratic convention, giving him a short window to announce his running mate.
The Republican convention begins Sept. 1.
