pp. Transferring music or other content to a cell phone using the cell phone provider's network.
Other Forms
Carriers initially prohibited the practice of allowing users to transfer existing music from their personal digital libraries to MP3-capable phones — a process known as "sideloading" — but they are now warming up to the idea.

Motorola's iTunes ROKR phone is the latest and best-publicized example. Cingular is not only supporting the sideloading capabilities, it is encouraging it with a rash of TV, billboard and print ads mimicking Apple's successful iTunes/iPod campaign.
—Antony Bruno, “The Next Move for Mobile Music,” Billboard, October 01, 2005
Consumers in Japan, South Korea and Great Britain are already transferring songs directly from their computers to their phones, a practice known as sideloading, or downloading full-length tracks over their mobile networks.

Ringtones may be big in the United States now, but full-track downloads and sideloading are the future, said Thomas Hesse, president of global digital business at Sony-BMG Entertainment.
—Alex Veiga, “Wireless carriers banking on mobile music,” The Associated Press, September 23, 2005
2005 (earliest)
With the industry now adjusted to the concept of paid-for downloads, high street chains are steeling themselves against new claims on their market share. That may mean consumers "sideloading" from their digital provider to their mobile phone (witness Napster's new partnership with Ericsson, and iTunes' association with Motorola).
—Paul Sexton, “Storm in a coffee shop,” Financial Times (London), June 21, 2005
An exclusive feature of the myplay service, myplay’s "Copy To Locker" technology allows the user to "sideload" tracks from partner sites directly into their Locker. Unlike uploading or downloading, "Copy To Locker" transfers the music file instantly from server to server, eliminating lengthy and complicated downloading processes. This makes it easy for the consumer to rapidly build an online music collection from a variety of sources.
—“New myplay free tracks include Fastball's 'You're an Ocean',” Corporate News Net, October 23, 2000