After a whole day at 800 Mhz, i tried to flash the 900 Mhz one, but the phone does not even power up. Charging was also dead, the orange led did not blink.
Fortunately, the update mode worked ok, and i was able to flash back the 800 Mhz.
I also tried 850 Mhz = restart during boot.
Now im on 825 Mhz
Well, better than nothing, but im little sad to see everyone has 900 Mhz without any problems.
// sorry for english