I did not know that yesterday!

AT&T introduced this toll-free area code in 1967, and as 1-800 numbers received seven million calls that year, quite a few companies must have participated. A Fast Company article mentions Amtrak and the airlines as early 800 customers.

Since the original system wasn't nationwide in the US, big companies had to maintain separate toll-free numbers for each geographic area in which they operated. By 1999, 30 billion toll-free calls criss-crossed the system. When the government broke up AT&T in 1984, new long-distance carriers were assigned blocks of 800 numbers, nontransferable if customers switched to another service. In 1993, by FCC ruling, 800
numbers became "portable," meaning they remained with their "owners" no matter which long-distance company provided the service. This precipitated a run on the 1-800 market, as businesses had found the right number could be a substantial advantage. (Think 1-800-FLOWERS, which generated 13 million calls in 1999.)

Though eight million possible 1-800 numbers exist, several factors eventually caused a shortage: a dramatic decrease in cost, increased competition, and even 1-800 use by individuals and families replacing the traditional "collect call." In 1996, the industry added another eight million numbers with the introduction of the 888 area code. 877 came online in 1998, 866 in 1999. If demand keeps up, you can expect more confusion with the rollout of 855, 844, 833, and 822 prefixes, all slated for toll-free duty.