It bothers me because:
- I live in a big city, so the infrastructure is pretty good and signal strenght is at 100% even at 3.5g.
- It happens ONLY on my N900 (and I have pretty few other various devices using the same operator's network, including 2 usb modems for computers, one netbook with builtin modem and one more mobile).
- It doesn't happen when I take the same sim card to different device.

I wil try a different sim card in this phone, I feel stupid for not thinking about this earlier... Nonetheless, what could I do if this specific configuration (this sim + my N900) doesn't work, but all other configurations (N900 + any other sim card or this sim card + any other device) work? Would changing sim card for a new one (but with the same number... I mean I get a duplicate of this one) make a difference?

I know about problems with WiFi and I also sometimes have them, but this is different - for me the problem looks like my N900 fails to switch from 3g to 3.5g at some point (I would like to know the cause...). I will let you guys know after trying with different sim card

Edit: and thanks for your input!