[EGreg]

How did WhatsApp introduce messaging? We already had messaging apps for years, including Skype, Facebook Messenger, iMessages, BBM and so on.

I think WhatsApp just made a rock-solid basic product that cost $1 a year after the first year, and that was its appeal.

[rak00n]

No, it was universality. WhatsApp had apps for all type of phone platforms including symbian, blackberry and even Tizen. Your friends could be on it despite whatever phones they're using.