I stand corrected - obviously, you don't need to have reception of a cellular network in order to receieve GPS positional info. I don't know if this was changed in firmware 2.0.1, but nevertheless, it works!
Until now, all I did was some tests using different SIM modules and the flight mode. The obvious thing, just testing it without a SIM, didn't come to my mind (probably because you just can't run most mobile phones without one).
Well, yesterday I tested my iPhone without using a SIM, and - behold - there was GPS! I checked that there was no cellular reception, using the cellular network monitor (dialling *3001#12345#*).
So it seems that Apple disables anything that has to do with radio using the flight mode, even GPS. The funny thing is, though, that you still can enable WiFi using the flight mode, but there is no way to do so with GPS.
So, sorry to all of whom I might have confused, cellular network reception is of no matter to GPS on the iPhone.