While MJ was being developed, Mobile phone and network people were inventing and upgrading ways of communicating with mobile phones. "Standards" were evolving, so MJ was trying to hit a moving target.
MJ support is in 4 flavours; iPhone, XHTML, CHTML, WAP
One of the earliest protocols was WAP Wireless Application protocol, which allowed text and button pushing to choose options. Then came imode, a protocol which allowed web access, email and data access. imode shared some things with chtml (fixed internet data formats based on HTML), and the option in MJ is evolving to be called CHTML but you can still see the imode name in various places. (imode was used in Japan). The people supporting websites have a problem in that there are a lot of the early style mobile phones out there (and visiting websites), but they will never be able to do what the later phones can do. As phones got more software and more memory and touch screens and so on, so the protocols to communicate with them had to evolve or get a new protocol with all the wizzy options. XHTML was developed for these types of phones. And then there is the iPhone which is different. BUT people with phones want them to do all the things that other makes of phone can do. So XHTML based phones can understand iPhone protocols. But chtml/imode and WAP are not capable of using those protocols.
Hope that helps.