It may be obvious to someone else, but I'd like to know how they detect a photo or video being sent, rather than text? WhatsApp is end-to-end encrypted, so they can't be proxying the data to the servers. Are they just guessing from the total data transfer seen from the subscriber?

There's a lot of unanswered questions. The CEO appears to have a fairly poor track record of running this kind of freemium global-SIM project, too, having done some digging. I'll watch with interest.