It would also be no more or less useful than just speaking. Do Japanese people carry around flash cards with kanji on them to disambiguate their speech?
There are non verbal cues or different nuances in inflection that help disambiguate. There's also situational context.
Furthermore, people use simpler language when speaking then when writing.
In Chinese, which has even more homophones, it is quite difficult to tease out the meaning of a passage written phonetically (in hanyu pinyin). When speaking and there is a word out of context (such as a name), it is necessary to explicitly disambiguate by putting the word in a common phrase or describing the characters constituent parts. For instance, I would introduce my self as "Zhe as in 'philosophy', Hao which is 'sun' on top of 'sky'".
It's actually not uncommon when speaking to have to either draw a kanji in the air, or refer to the symbol you mean by cross-referencing another word that uses it to disambiguate.
