Thanks for your reply. I appreciate the help.
Actually no, this is not correct: ANY preinstalled japanese softbank apps (as any other bloatware) can be removed and won't keep running in the cached services. All you need is root access and a bloatware removal tool (I use Titanium Backup Pro - Bloatware Melt Away tool - it even removed the Softbank logo at startup!).
I actually loooked in the market for the Softbank Mail app, to re-install it, to apply Tokyo_Dom's fix for MMS, which - by the way - worked perfectly. But I don't have a lot of time to test removing it again etc.. and I don't want to keep it. So I was hoping that someone had already tried to remove it after applying the tweaks to see if MMS would keep working. Anyone?
But, cheeseus, anyway, thanks for replying! Appreciated!