Guys, i had the same problem just now, well, the solution to this matter is with holding the lock button and the home button the same time for 10 seconds and it will turn the iPhone off, then press and hold the lock(top) button for 3-6 seconds and turn it on, screen back to normal! :)

I've come across this problem a couple of times recently here are some steps I have taken -

For 3GS

1. Reset the phone often solves the problem and restore if still no joy.

2. Swap with a known working screen but install the working one with the board powered down, if still a white ecreen then I assume I am on the board.

3. Check the LCD connector on the board just south of the camera -remove board and refresh solder if necessary and check under high magnification for solder bridging - recheck with good LCD - if still white

4. Remove the shielding from the components at the top (SIM end) of the board - using a rework station get the whole board to 100 c for five mins and then to 150 c for five mins and then to 190 c - using hot air at 232 c warm up the chips just south of the LCD connector - when warm enough I drop in some liquid flux using a dropper.

Let cool by keeping some heat on the whole board but reducing in 50c decrements - leave for half an hour - and put it all back together three intractible white screens I have solved by reliquifying the solder - all of the phones had signs of being dropped badly - I would suggest that the worst cases had fractured some connectors under the display chip.

if its only 4 months old id take it back to the apple store.

I would demand a replacement while they are fixing your old unit. I for sure wouldn't pay for service that I'm not getting. Who knows when they will replace it.

@#!# of iphone 3gs

Thank guys. I held the home and turn off button for ten seconds and wha la, back to new.