I shan't pretend to have perfect pitch but I think I have a pretty shrewd idea that a good way to aquire it would involve singing notes because this way the pitch sensation is registered in terms that are set by what your vocal chords can do. For instance I know that the lowest note I can hit is an A on the open 5th string. Perhaps it might help a person pick up tunes if they hum to it, translating the pitches into a sensation which, being felt at different heights in the vocal tract depending on the frequency of the noise might make the task of assesing its pitch easier.