The only missing function for my first BlackBerry was the ability to view and input Japanese using my Curve. After looking around these forums and on the web, I found two working options and thought I'd share them here. Unfortunately they are both subscription based so if you really need it like me, I feel it is worth it.
[Namimail]
NTT DoCoMo USA Namikiteru Wi Fi & Namimail for BlackBerry
This software is from NTT DoCoMo USA and they have two versions. Namimail 1.2.4 is a new version that just came out for BIS 2.3 but although input was OK, viewing did have some glitches. They also have Namimail version 2.X which is the better version regarding input simplicity and is only supported for BlackBerry devices with Japanese fonts installed available for sale in the Asia market. Of course with the new OS out with CJK support for the Curve, I tried it and it worked perfectly.
You will first have to download the recent OS that supports Chinese/Japanese/Korean viewing. You will find a sticky with the information on where to download and how to install it on this forum. After installing and subscribing to their service, instead of downloading the 1.2.4 version via OTA, log into your account via the web (PC) and download the version that says Japan/Hong Kong/Singapore markets. Unzip the file and install it via the Desktop Manager.
That's it! It works flawlessly. They do have some minor bugs that hasn't really affected me but please check the website. You can try it now for a free 30 day trial so you can always cancel if you don't like it but I doubt you will. The reps there will tell you that they will not be responsible for any damage as they do not have it listed for compatibility with the Curve and I too cannot take responsibility if it damages your BlackBerry. That goes for the solution below too.
[METAmessage Language Support]
METAmessage for Wireless - BlackBerry Software, Spell Check Email, Print Attachments, Print Messages, Listen Voicemail Attachments
This software I found on I believe Handango. You can install this via OTA but when you first use it, it will need to activate. They send you an email that has an attachment that supposedly activates the software but after numerous attempts I never was able to receive it. I did receive it on my Outlook so I did a forward email and removed FW: from the subject line and also removed the Original Message text that Outlook adds and just left the code the original email had and sent it to myself.
Doing it this way I was able to receive the email which activates the software and deletes itself automatically. The Japanese viewing is fine but I prefer the fonts that from the CJK OS. The input is OK but the dictionary is limited and sometimes you have to type one character at a time to get what you want.
The site says it does not support the Curve but a few people got it to work like me.
[Conclusion]
With the only two options that are currently available, I recommend Namimail using the 2.X version with the CJK supported OS. You do have to call them to subscribe and it might be better if you spoke Japanese as the few people I talked to, they were all Japanese.
I have been using it for a day now without any problems and hope this will will help some people that are in need of Japanese view and especially input.