Re:The earliest "digital" mass service (Score 1)

Ceefax (or equivalents on other, non BBC channels) were indeed interactive. I have played quite a few games via this service which basically involved you dialling a number and navigating to the page you get told on the phone. From there, you can press buttons on the phone and watch the content change within a second later.

There were even one or two banks that allowed for online banking via Teletext (ITV's equivalent to Ceefax). If you couldn't afford the phone bill, it was always fun to navigate to pages blindly to see information on other peoples' accounts, so it arguably wasn't the best idea!