ChatON is Samsung's own proprietary mobile messenger service, available in multiple countries (237 stated on the store page) and supports 63 languages. As one could imagine, it's fairly popular. Available on iOS, Android and the web, Samsung has now made ChatON available to all Windows Phone consumers, instead of restricting it to those who own a Samsung smartphone.
You'll need a Samsung account to get started, but after that's squared away you'll be able to enjoy chatting with friends and group action. It's not a bad app and Samsung has been releasing numerous updates for its collection of Windows Phone software, so we recommend you check it out if you have friends that utilise the service on other platforms.