I'VE GOT THE SOLUTION!!!!
Just push up all that tiny damned contacts on the phone and everything turns ok!
They are the connection to the microstrip antennas on the back of the phone. I don't know the location of bluetooth/wifi chipset (I believe it's the one on the top left). I've just pushed up all the contacts for not having any doubt
. I did it very gently with a plastic screwdriver.
Now I've got full wifi bars in the router's room and a stronger signal all over the house!
Bluetooth headset now works great! I'm so excited!!!!
The only problem about this fix is that you need to remove the little white sticker on the top right screw, and I believe that this will invalidate warranty. I put it back where it was after I operated on the contacts...seems to be ok, but It also seems to be reproducible with another common white sticker if It's really a problem for warranty.
Anyway, tomorrow I'll compare my phone with my friend's one, that has no reception problems, using Wifi Analyzer. This will be the definitive test for the solution.
Thanks for the picture, Kennyli! It opened my mind!
Edited by costan1986, 12 January 2011 - 10:47 PM.