18. The method of claim 17 , wherein the step (d) determination is carried out by calculating an average of the plurality of confidence scores and setting the user-specific confidence threshold to a value greater than or equal to the calculated average.
18. The method of claim 17 , wherein the step (d) determination is carried out by calculating an average of the plurality of confidence scores and setting the user-specific confidence threshold to a value greater than or equal to the calculated average. 19. The method of claim 18 , wherein the at least one user-specific characteristic also includes pitch and at least one formant of the utterance, and wherein the user-specific confidence threshold is also determined using a multiple regression calculation including the pitch and the at least one formant of the utterance, and a pitch coefficient and at least one formant coefficient developed from a plurality of development speakers.