When a person explains that she is "all ears," she is using an idiom that indicates that she is willing to pay attention to what someone else is saying. The speaker is also typically indicating that she is open to actively considering the other person's words. In some cases, the expression of "all ears" simply indicates that the listener has the time and interest to listen to another, though it may also indicate an over-eagerness to listen to unsavory news or information. It may also be a plea for information from someone who is faced with a difficult challenge.
While the expression "I am all ears" may initially conjure up the image of a body that is suddenly overwhelmed by very large ears, in its most literal sense, people use the term to convey a desire to hear. The desire or interest is strong enough that the speaker essentially notes that, for the time being, he is willing to channel his attention into his auditory capacity. It should be noted, however, that the term is sometimes used by individuals in writing as well. Even though people do not actually hear the written word, the meaning of the idiom remains the same. A recipient of written communication is willing to pay attention to whatever the writer wishes to communicate.
The context in which "I'm all ears" is used often contributes to its tone or meaning. In some incidences, it is kindly meant, intended to convey to someone in distress that the listener is happy to pay her attention so that she can express her concerns. In other cases, it may reflect a morbid or less wholesome curiosity about gossip. Finally, it can be an expression of frustration by the listener, who has encountered a difficult situation or problem for which he has not found a solution. As such, he is very open and interested in listening to someone who may be able to help him achieve a resolution.
In United States, "I'm all ears" got significant media attention when it was used by 1992 presidential election candidate H. Ross Perot. During a debate, Mr. Perot used the phrase in response to a comment made by one of his opponents. Mr. Perot had very large ears and, as he wore his hair very short, they were certainly a prominent feature. After he used the phrase, the audience became very amused, and for a few days the media made numerous comments about Mr. Perot's fortunate and apt choice of words.