Whatever device I end up buying, it’d be nice if I could use Japanese on it. It’s not a hard requirement, but it would sure make things more interesting. Unfortunately, getting Japanese to work on an American or European device involves quite a bit of work, but there are people who manage to get it working. The approaches vary:

• Treo 650: There seems to be a long history of hacking PalmOS to support Japanese. The two leading candidates for packages that try to do this seem to be “J-OS” and “JaPon”. I’m not sure how the former works, but the latter appears to work by re-implementing some of the PalmOS API’s, so that programs can call in with functions containing Japanese encodings. This apparently also lets you use the Japanese input method ATOK for Palm OS, which is a huge plus. There is also another FEP available, called “POBox” which works with the Palm. There also seems to be a package called “CJKOS” which does similar thing as “J-OS” but for Chinese, Japanese, and Korean. Unfortunately, that one doesn’t have very good input method support.
• Cingular 2125: I thought WinCE might be a bit better about doing stuff in unicode, but apparently it isn’t. The software here is called CE-Star, and it reminds me of “NJStar” that used to be around for Windows way back when (maybe it still is). The principle being that, you hook rendering calls, and then figure out character encoding on the fly and render the appropriate glyphs. This works, surprisingly well, but it fails in certain key situations, like when applications try to do their own word wrapping (because they compute character positioning based on no knowledge of the actual glyphs they get rendered in.) There apparently is a way to replace the system font with a Japanese one without using too many hacktastic techniques (a registry edit), but it doesn’t seem like there’s a way to change the default character set encoding like there is on desktop Windows XP.
• Nokia/Symbian: Architecturally, Symbian has the best support for Japanese display and input. Internally, everything is unicode. Unicode fonts with Japanese glyphs are easy to install. It even has a “FEP” framework that lets you add in new input methods. There’s even a version of ATOK that runs on symbian that ships with certain Japanese FOMA phones. Apps that are written correctly should be able to display Japanese content without too much work. There seems to be no availability of a Japanese input method however, which is irritating. There is one Nokia Series 60 phone that came out in Japan under the vodaphone label (its a 6680) which has some kind of Japanese input support. I’m not sure if its possible to pull the bits out of that phone, and load it on another. I think adding FEP’s is possible, so maybe writing my own is within the realm of possibility. Porting “anthy” for example. But Symbian phones will probably require the most work on my part. This might be fun, but it will be a while before anything works.

It seems like the two most likely options are: get the Treo and use the hacktastic stuff that lots of other people are using successfully, or get the Symbian and try to engineer my own solution.