My friend is asking me if he buys a new phone, can he downgrade it to 1.1.1 (including the baseband of course!)

Although I am under the impression this is not possible, I am not sure why since a jailbreaked 1.1.1 (which I know is possible) can use bbupdater to flash the baseband (presumable to a 1.1.1 baseband)

Any comments are appreciated.