Japanese e-commerce giant Rakuten has today announced its $900 million acquisition of Viber. The hugely popular messaging and VoIP service will help Rakuten expand its digital ecosystem even further, and it marks its first foray into voice communication.

With over 300 million users in 193 countries, Viber will also strengthen Rakuten’s presence outside of Japan. The free service was founded in 2010 has become hugely popular across mobile devices for instant messaging and video calling. It grew over 120 percent in 2013.

Not only will it put Rakuten in touch with new users, then, but it will also help Viber step up its battle against rivals like WhatsApp and Skype.

“Viber understands how people actually want to engage and have built the only service that truly delivers on all fronts,” said Rakuten Chairman and CEO, Hiroshi Mikitani, in a statement today. “This makes Viber the ideal total consumer engagement platform for Rakuten as we seek to bring our deep understanding of the consumer to vast new audiences through our dynamic ecosystem of Internet Services.”

Rakuten’s primary business is its online shopping mall that consists of tens of thousands of merchants, as well as a digital travel service and an online bank. It generates around ¥400 billion ($39 billion) in annual revenue, but its dominance in Japan is increasingly under threat from companies like Amazon.

Viber isn’t the only service Rakuten has splashed its cash on in an effort to expand its online presence, however; it also made a major investment in Pinterest back in 2012, and acquired Canadian e-book retailer Kobo for $315 million in 2011.

• SourceBusiness Wire