Hiroshi Mikitani, chief executive officer of the Japanese e-commerce company Rakuten Inc. (4755), aims to expand to 2 billion users with his acquisition of messaging service Viber Media Inc.

Growth for Viber’s free messaging and Internet calling app is already accelerating. It’s adding 600,000 users daily, up by about 50,000 from Feb. 14 when the deal was announced, and that can rise to a million a day, Mikitani said in an interview. Viber had about 300 million users at the time of the deal.

Mikitani, 48, is plowing cash into technologies such as mobile applications and online video as he seeks to expand Rakuten beyond its core business as an online marketplace. The strategy has led to rising competition with companies such as SoftBank Corp. (9984), Amazon.com Inc. and Facebook Inc. (FB), which agreed to pay $19 billion for the messaging service WhatsApp just five days after Rakuten unveiled its deal.

Viber is a good messaging service but competition in very tough in this arena so it will be interesting to see how this unfolds.

More at Bloomberg.