Essentially, those spectacular mobile internet subscriber numbers published by NTT DoCoMo may be overstated. A typical Japanese user ordering mobile phone service from NTT DoCoMo for the first time will usually be subscribed to the i-mode service unless he or she specifically refuses the extra online service. Mobile phone retailers have a strong incentive to push for the online bundled service because they in turn receive a generous rebate from NTT DoCoMo. Thus, most of the time a mobile phone subscriber will end up paying for the i-mode service whether they actually use it or not. Revenue from voice traffic is still the main source of income for mobile operators.
Data traffic generating by e-mail also accounts for a significant portion of the revenues.
According to a research done by NTT DoCoMo, e-mail usage is positively correlated with voice usage. The increase in usage of e-mail actually drives up the amount of voice call traffic. The latest subscriber number reported from NTT DoCoMo stands at 21.7 million. That brings the total number of active i-mode mobile internet users to approximately 17.4 million. While in no way is DoCoMo's extraordinary success questionable, in order to get an accurate view of Japan's mobile market it is necessary to look at the differences that may arise when defining subscribers and users.