The US did have SMS caps/charges, but pre-2008-iPhone+AppStore. (from memory) Consequently, I don't remember much of a timespan when US customers had both (a)

The US did have SMS caps/charges, but pre-2008-iPhone+AppStore. (from memory) Consequently, I don't remember much of a timespan when US customers had both (a) SMS caps/charges and (b) smartphones with open-enough app stores to distribute something like WhatsApp. For much of the rest of the world, including international communication, that was a more extended period.