If you're using C6903 then you have to flash the modem file as well (download it somewhere in the thread and do the adb sideload in recovery).
1) Flashed v2.5
2) Wiped data, cache, dalvik.
3) Flashed v3.0
4) Didn't wipe anything
In Thailand, almost everybody are using GSM (some may also use LTE but that's not the point here). Maguro is well supported by all major carriers -- DTAC, TrueMove, and AIS -- I have tested all of them :).
You can get a prepaid sim card from an...