Japan's Rakuten is acquiring messaging and VoIP company Viber for $900 million, the Internet services companies announced today.

This is the fourth big-ticket acquisition by Rakuten, following its acquisitions of Kobo, Wuaki.tv, and Viki.

Viber is one of the most popular mobile communications services worldwide with a rapidly growing global user base of 300 million registered users, growing over 120% in 2013.

Rakuten said Viber 'perfectly complements Rakuten's strategy in the digital space'. The combination also unlocks massive new potential markets for Viber through Rakuten Group's roughly 225 million global members.

With 40 different services, Rakuten has built one of the world's most robust and dynamic Internet services ecosystems, centred around a unified ID membership database that features the enormously popular and successful online Rakuten Super Points rewards program. Viber's fun approach to messaging and high quality VoIP services is a perfect marriage with Rakuten's digital content offerings and its "Shopping is Entertainment" philosophy laying the foundation for the world's most comprehensive and engaging daily online platform, the company said in its statement.

"Simply put, 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. "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 is one of the world's most important Internet companies," said Viber CEO and Founder, Talmon Marco. "It is truly dominant in its home market of Japan and has been rapidly expanding globally. This combination presents an amazing opportunity for Viber to enhance our rapid user growth in both existing and new markets. Sharing similar aspirations with Rakuten, our vision is to be the world's No.1 communications platform and our combination with Rakuten is an important step in that direction."