Instant messaging is emerging as a favorite communication tool among teenagers and young adults, with a good number of them sending more IMs than emails, a new survey says. Nearly 66 percent of 13- to 21-year-olds say they send more IMs than emails, compared with 49 percent last year, according to an America Online-commissioned study of instant messaging trends. Overall, 38 percent of users say they send as many or more IMs than emails.