imode is available only in Japan, whereas Europe and other big markets for 3G mobile service providers are completely WAP-based. In the United States, most service providers have chosen WAP.
The most basic difference between imode and WAP is the different graphic capabilities; imode only supports simple graphics, which is far more than what WAP allows. The imode packet-switched data network is more suited for transferring data than the WAP CS network.
Another major difference is the “ always-on ” capabilities of imode. Since users are not charged for the time they spend on-line, it is more convenient and also less expensive. Since there is no need to dial up before using the various IP-based services, e-mail becomes as instant as SMS. imode uses cHTML, a subset of HTML, while WAP uses WML, a subset of XML. cHTML, while certainly easier to develop from a web-designer standpoint, has its limitations. The downside of WML, on the other hand, is similarly obvious — currently a WAP gateway is required to translate between HTML and WML for almost every data transfer. On the other hand, since WML is derived from XML, it is much more extensible. XML allows for more dynamic content and various different applications. In the future, a WML-based service will be of more advantage than an HTML-based one. So while WAP may currently require more complicated technology, in the long run, it may enable the user to do more with his or her device.
Source of Information : Elsevier Wireless Networking Complete