The deal, to be announced Wednesday, comes two weeks after Falcon 9 reached orbit on its maiden test flight.
Iridium previously announced plans to replace its current satellite network by launching six dozen next-generation satellites between 2015 and 2017 at a cost of $2.9 billion. The company, which covers the whole world, uses the satellites to provide voice and data services for commercial and government clients.
Neither company would say how many Falcon 9 launches would be required to put the satellites into low-Earth orbit from Vandenberg Air Force Base, Calif. Each rocket launch will carry multiple satellites into space.
"It's a perfect marriage," Iridium chief executive Matt Desch said of the agreement with SpaceX.
While SpaceX will be the main launch provider, Iridium expects to sign with at least one more rocket maker.
SpaceX — or Space Exploration Technologies — is run by PayPal founder Elon Musk. NASA hopes to use SpaceX to haul supplies and possibly astronauts to the International Space Station once the space shuttles retire.
Musk called the Iridium deal "a very big endorsement." The satellite phone company had its choice of international launch providers, but ultimately chose Hawthorne, Calif.-based SpaceX.
"Falcon 9 is the vehicle of choice both for the federal government and the commercial sector," Musk said.