Apple is to produce a version of its iTunes online music downloading service which will be compatible with Motorola mobile phones.
Apple has sold more than 100m tracks on its iTunes online store
Under the deal, Motorola phones will be able to install songs from iTunes via a USB cable or Bluetooth connection.
Apple said the new iTunes music player would become Motorola's standard music application for its music phones.
Motorola - the world's second biggest mobile phone maker - said the music handsets would be available from 2005.
Financial details of the deal between the two US firms were not disclosed.
Apple has sold more than 4 million of its iPod digital music players, and more than 100 million tracks on its iTunes online music store, since last April.
The firm launched iTunes in the UK, Germany and France in June.
The mobile market is already a major target for the music business, which makes increasing amounts of money through selling ringtones.
Steve Jobs, Apple's chief executive, said the 1.5 billion mobile subscribers expected worldwide by the end of 2004 offered a "phenomenal opportunity to get iTunes in the hands of even more music lovers around the world".
The initiative would make the digital music revolution a reality for many more people, Mr Jobs stressed.
"Wouldn't it be great if you could take a dozen of your favourite songs with you on your phone?," he said.
Ed Zander, Motorola's chairman and chief executive officer, said the deal was a "natural partnership" between two like-minded companies.
"Being able to transfer songs you have purchased from iTunes to Motorola mobile handsets expands the market reach for both of us, delivering an amazing music experience to millions of wireless users," he said.
"People want to stay connected to the ones they love, the information they need and the gadgets that keep their lives humming and we are making it possible."
Shares in Apple rose 56 cents to close at $31.26 at the end of US trade on Monday. Shares in Motorola rose 14 cents to close at $15.42.