One who listens in on others without getting caught. A true ear hustler does not let everyone know that he has heard what he heard, and retains the information for future references.
Someone who eavesdrops (usually in an office setting) and uses the information gathered to their advantage, often to the detriment of others.
My co-worker Bruce feels totally threatened by me. He listens in when I'm on the phone with my man and he told our boss that I was making personal calls at work. That ear hustler wants my job! He even told our supervisor that I'm planning to call in sick tomorrow.