It's more akin to a web browser in the dial-up era (from both the pricing and technical standpoints). Or any of the paid phone services (porn, alarm) or texting services (buy ringtones, ...) of the same period.
Also what was French voice phone service billed like back then? Did you have to pay per minute for non-local calls (or all calls, even)?
That's incorrect. There was a dialer on later versions of Minitel. And while you could technically set up a V23 BBS-like server behind a regular phone line to talk to Minitel terminals, the whole business model relied on the use of premium short numbers (361X) whose revenue was shared between France Telecom and service providers.
It was absolutely an App Store model and fortunes were made at that time.