just realised that /mnt isn't empty, so that was a foolish attempt, but it wasn't the problem:

Nokia-N800-50-2:/home/user/bin# mkdir /mnt2
Nokia-N800-50-2:/home/user/bin# mount -r /dev/mmcblk1p2 /mnt2
mount: mounting /dev/mmcblk1p2 on /mnt2 failed
Nokia-N800-50-2:/home/user/bin# mount | grep mnt2
Nokia-N800-50-2:/home/user/bin# mount -r -t ext2 /dev/mmcblk1p2 /mnt2
mount: mounting /dev/mmcblk1p2 on /mnt2 failed