This supposedly works for people who have guarantees and want to know what cabin they have been assined...I'm not sure which lines it has worked on except Carnival.
Go to Carnivalīs website and go to the Gifts and Services section. Proceed like you an going to enter the info. Enter your booking number. Then starting with the category guarantee you have, start entering cabins numbers (you might need a Carnival brochure for this). Once you have entered all the cabins in your category of guarantee, enter the next category up and so on until you find your cabin. It doesn't work all of the time and it's very time intensive.