yes, this method exist, i have even used one, though its not exactly the fastest method.
however, if you can read chinese (however, may not understand the principal of strokes and character formation, hence most methods using keypads or keybroad will be hard and slow to use) , phonetic cantonese input is one method which i find the best
Online Cantonese Input Method 網上廣東話輸入法
every person prefer a different method suited to them