Plenty have been wondering what's next for WhatsApp after the popular messaging service was purchased by Facebook for $16 billion last week, and now we have the answer: voice calls. According to TechCrunch, WhatsApp announced during a Mobile World Congress event today that it would be adding voice services to iOS and Android during the second quarter of the year. The feature will reportedly head to Nokia devices and BlackBerrys sometime after that.

Now at 465 million monthly active users

WhatsApp also provided an update on its active user count: it now has 465 million monthly active users and 330 million daily users, according to TechCrunch. That's 15 million more monthly users than Facebook detailed just last week when reporting the purchase. WhatsApp has already risen to an impressive popularity on basic messaging features alone, and the addition of voice calls should only enhance that further when they begin to roll out later this year. The app has done well by offering inexpensive messaging services where messaging is traditionally quite expensive, and doing the same for phone calls would likely be a boon for growth. WhatsApp is reportedly optimizing the amount of data its voice calls use, which should help in keeping users' expenses down as well.

The Guardian reports that WhatsApp's voice calling features will be free, though it's possible that this may only be for a limited time. Messaging is initially free within the app, but eventually requires a $0.99 per year subscription. It's likely that voice services will fall under this too, while breaking it out as a second offering could even provide an additional revenue stream. Though WhatsApp has never appeared eager to bother users with added costs like that on the path to big profits, it'll be interesting to see if that changes as a public company underneath Facebook.