“The worth to a company to have the president always talking about a BlackBerry and how it absolutely is a necessity to keep in touch with reality?” he said. “Think about how far the company has come if they’re able to say, ‘The president has to have this to keep in touch.’ ”

Image President-elect Barack Obama says, Im still clinging to my BlackBerry. Credit... Charles Dharapak/Associated Press

The maker of the BlackBerry, Research in Motion, recently introduced advertising campaigns and products like the touch-screen Storm that are meant to position BlackBerry as not just a business device but a consumer product like the iPhone. The company, which declined to comment on Mr. Obama’s enthusiasm for its product, also struck a sponsorship deal with John Mayer, a popular guitarist but hardly the leader of the free world.

“The most powerful man in the country is saying, at this moment, basically, I can’t live without mine,” Lori Sale, the head of artist marketing at the agency Paradigm, which pairs actors like Adrien Brody and Katherine Heigl with advertisers. “It represents their now complete and final crossover to a device that people adore.”

Ms. Sale said that Mr. Obama had essentially participated in what is called a satellite media tour for BlackBerry by discussing the product with reporters. Just a single day of a media tour, “with the most A-list of A-list of A-list, would probably be 10 to 15 million dollars,” she said.

That he is not paid to promote BlackBerry is even better for R.I.M. “What makes it even more valuable than that is how authentic it is,” she said.

Mr. Kelly said the endorsement went both ways: while Mr. Obama was doing a lot for BlackBerry, BlackBerry had helped Mr. Obama’s image by making his message seem more relevant.