I think mass produced postcards were a bit more widespread than stone tablets or even papyrus , although it is subjective. The postcard had the huge advantage that it was cheap, relatively quick to send, sometimes 6+ daily deliveries in major cities, and you didn't need a high level of education to use it. It was the perfect combination of mass production, cottage industries and user generated content, similar to the internet today. So you can't really compare it with Ancient Greece.
