Wikipedia
GameLine was a dialup game distribution service for the Atari 2600, developed and operated by Control Video Corporation (CVC). Subscribers could install the proprietary modem and storage cartridge in their home game console, accessing the GameLine service to download games over a telephone line. GameLine is notable for its exclusive selection of games, and for its pioneering business model which eventually gave rise to America Online.
In the early 1980s, a cable pioneer named William von Meister was looking for a way to use his innovative modem transmission technology, which was previously acquired in ill-fated attempts of sending music to cable companies. Legal issues caused cable providers to step away from the service, leaving Von Meister with a delivery tool and no content.
He then converted his variable speed adaptive modem technology to download games from central servers to individual households. This allowed users to dial a system and, for a fee, download games to their GameLine modules. The game would typically work for 5-10 plays, after which the user would have to connect to GameLine again and pay for another download.
The "Master Module" physically resembles an oversized silver Atari cartridge. It has a phone jack on the side that was used to link the Master Module with the CVC computers. The module is able to transmit with pulse or tone dialing, allowing the unit to be versatile in the field. The games available on the GameLine service were all from third-party gamemakers, the largest of which was Imagic (whose catalog is now controlled by Activision). CVC tried, but failed to obtain licensing agreements from the largest game makers, such as Atari, Activision, Coleco, Mattel, and Parker Brothers.