(Telecompaper) Japanese e-commerce group Rakuten has agreed to buy the mobile messaging service Viber for USD 900 million. Rakuten said the deal supports its expansion in the digital content space, following its acquisitions of Kobo, Wuaki.tv and Viki. Viber's messaging and VoIP services can be offered to the some 225 million customers of Rakuten's other web services, joining its 'Super Points' rewards programmes. Rakuten said it also sees potential to expand Viber's stickers platform and develop it as a gaming service, similar to the rival Japanese messaging service Line. Viber has over 300 million registered users worldwide, after growing over 120 percent in 2013.