NTT DoCoMo is Japan's largest mobile phone company with around 51 million subscribers.
RIM co-chief executive Jim Balsillie told Reuters that the company is eager to enter the Japanese market because it has such a large corporate presence.
Figures for the sales expectations for Japan will be included in RIM's upcoming financial results on 29 June.
Balsillie said that RIM has now launched services with 170 carriers around the world and has plans to launch with a further 140.
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