WarGames/WMG

The movie's set Twenty Minutes Into the Future (of 1983).

 * The Ordinary High School Student has an in-home internet connection at a time when many universities didn't.
 * He had an acoustic modem he'd salvaged out of the garbage of a computer company. At that point all he needs is an ordinary phone line.
 * He buys an airline ticket online almost 10 years before commercial use of the internet was enabled (and never gave credit card info, real or stolen).
 * Of course, by that time...
 * He'd hacked into the airline company's reservation computer, the same one that ticket agents access through terminals. It wasn't intended for consumer use. (This is also why he didn't have to give payment info; he was stealing the ticket.)
 * The movie specifically points out in-dialogue that he did not have an actual plane ticket -- he'd merely made a reservation.
 * According to Todd Fischer of Fischer-Freitas (which supplied Dave's IMSAI computer), "This early version of the script (sent by the Product Placement facilitator) had the story line placed in the future and seemed to depend more on fantasy and conjecture rather than technical reality."