Often, people says "Picture speaks a thousands words"

I agree with that, strongly.

Sometimes the work requirement is to deal with people via email.

But sometimes I'd need to write a whole grandmother long story to explain a situation - which people will still reply me with even more questions.

Then, I would explain them via the phone - still, there were chances that they still don't 'get the picture'

Yes, picture, that's why I'd love to use diagram to explain the situation.

I don't mind to spend a bit time to draw out the diagram - that would really make my life easier, be it to explain, to discuss or to inform.