uhh guys i got some news. im on stock au-kddi rom from xhausx and i ran the cmail client update OTA again. market just updated, native japanese paid apps can be downloaded and installed with updates, google apps just updated, i can send/receive c-mail/sms now. need to go out for a while, will post more details later.
UPDATE:
from cgm7 i went to recovery (amon), did a backup on my current rom, wiped using calkulin's format all, then did a nandroid restore (again) of xhausx's stock au-kddi rom. once rebooted, sms/cmail was not possible, although market was ok. i went to check OTA updates, and a download was available for cmail. ive read somewhere in the thread that you can't do OTA's in this phase, but i did it anyway. it downloaded, i installed it, an it went to recovery by itself. from recovery, the installation screen sort of hung; i chose restart, then the screen suddenly said "flashing zip file", a very tense moment, then restarted. i'm like, what have i done?
at any rate, upon booting a congratulations note saying i had upgraded was on the screen. i could then use sms/cmail to send/receive messages, gps/wimax/wifi was ok, market updated itself (it was a relief to see the prices on apps back to yen instead of dollars again), japanese keyboard is back, downloaded paid apps and installed some, google apps (maps, gmail, etc) auto updated too. i am on froyo 2.2.1, and everything seems back to normal.
checked software updates again, and the gingerbread OTA was available. i chose not to update, because it's the reason i rooted my phone in the first place

i use yahoo messenger to chat with my wife and kids abroad; and updating caused the front cam not to work.
i also checked my CID, and it seems that it has reverted from sprint back to kddi; that's probably why i could use the local market again. as for the hboot, well...
-Revolutionary-
SUPERSONIC DVT1 SHIP S-OFF
HBOOT-6.16.1002
MICROP-041f
TOUCH PANEL-AMTEL224_20aa
RADIO-2.15.00.05.06
hboot is unchanged, and i still have s-off, which is curious because i can't run root explorer on my current stock rom. at the moment, it's fine enough for me

my phone is where i want it to be. i think
thanks to all the people in this thread for taking me on that wild ride xD and thanks to xhausx for making it possible to come back from it...sort of

i really do hope someone finds a way to resolve the issues using custom roms; im sorta missing CGM7 already!
cheers!