Well, that didn’t take long.  Less than a week after Facebook threw $19 billion at it, free messaging app WhatsApp has announced it’ll be offering free voice calls by autumn.

Co-founder Jan Koum made the announcement at Mobile World Conference, an annual gathering of execs in Barcelona.  He also revealed that WhatsApp has added 15 million active users since Facebook bought it, bringing its total to over 465 million per month.

Koum said: “We’re going to introduce voice on WhatsApp in the second quarter of this year… We think we have the best voice product out there. We use the least amount of bandwidth, and we optimise the hell out of it.”

The new service will be introduced for iPhone and Android first, with Windows Phone and BlackBerry to follow later.

One hopes there won’t be a repeat of this weekend’s antics, when WhatsApp experienced a surge in demand so great that their servers conked out, leading people to download rival app Telegram instead…which then also had a surge so great their servers did the binary equivalent of swooning like an 18th century heroine.