Banking transactions are transmitted over a leased line between DoCoMo's gateway servers and the bank, so sensitive data doesn't flow onto the Net at large. Likewise, DoCoMo collects fees on behalf of proprietary content and service providers, so payment, authorization, and accounting are all centrally managed. Designing for WAP incurs a not insignificant learning curve, so there are significant barriers to new sites going up. Also, in Japan, all WAP phones are preconfigured and there is no way to change default server configuration. In short, it appears that in Japan the network operators are the supreme gatekeepers controlling who gets in to their wireless gardens, zen-like in their simplicity of revenue model and content control.
Operators have a choice.
One reason for the success of NTT DoCoMo may be the fact that the i-mode walled garden is not entirely sealed off. Some operators realize that offering prospective users as much content as possible makes their services more popular, while allowing them to charge a premium for the preferred sites that provide users quick and efficient services via menu drill-down. Ultimately, mobile network operators and protocol composers alike will realize that it's in everyone's interests to offer as much content as possible to as many surfers who wish to access it. In other words, although mobile network operators might wish to control the platform, and all the content that goes into it, competition and customer demand for open access will eventually prevail. Moreover, we have several competing wireless networks.