I was thinking at the very least the hands free wouldn't work, or something. But after persuading the kind manageress of the local Vodafone store to sort me out a full size SIM (they had made some excuse not to give me one previously) I whacked it in and everything functions perfectly..
Admittedly this won't be used much but then again, I often find myself phoneless due to forgetting to charge my regular phone. And if you have the phone, its a bit daft to not bother making it functional.