there is a korean program called dodol. it's all in korean, but in the market, search for "dodol v2.3.10" and find the one with the red, blue, green bar graph icon.
you can put a widget on your home screen and it'll keep track of your data, minute, and txt usage (although it doesn't seem to work with txt on mine, it's always at 0)
it automatically restarts at the beginning of each month, so unless you dl it before the month begins, it will be inaccurate until the new month begins.
I don't know how accurate it is, i think it keeps track through the phone and not through you service provider.
anyways, hope this helps someone.