F.I.S.T. was basically a choose-your-own-adventure game that you played on your phone. Input was via the numbers on the keypad (or dial!); output was sound in your ear. This kind of game would still work well today if people made decent ones.
In the UK (where it began), it used premium telephone lines. Some children playing it racked up bills of thousands of pounds. This is why premium phone lines today always have to tell you how much you're being charged. As always, where games lead, the rest of the world follows.
I never played F.I.S.T. myself, because from my work with British Telecom for MUD I knew it would work out expensive to play.
Captain Atom seems a bit of a jerk, to be honest.