WhatsApp, the multi-platform messaging app used by over 250 million people per month, is now free to download for iOS users. Previously a $0.99 purchase, the price-drop brings the iPhone app in line with the Android version, which is also free to download. Just as on Android, you'll be able to use all the features of the app for 12 months, after which you'll have to pay $0.99 for an additional year's access. The move to a subscription model has been planned for some time, and doesn't affect anyone that's already using the app.