Zogby actually did a poll to measure this:
http://www.zogby.com/news/ReadNews.dbm?ID=919
“Polling firm Zogby International and partner Rock the Vote found Massachusetts Senator John Kerry leading President Bush 55% to 40% among 18-29 year-old likely voters in their first joint Rock the Vote Mobile political poll, conducted exclusively on mobile phones October 27 through 30, 2004. Independent Ralph Nader received 1.6%, while 4% remain undecided in the survey of 6,039 likely voters. The poll is centered on subscribers to the Rock the Vote Mobile (RTVMO) platform, a joint initiative of Rock the Vote and Motorola Inc. (for more information: http://www.rtvmo.com). The poll has margin of error of +/-1.2 percentage points.”
However, if I were Kerry I wouldn’t get too overjoyed, given that young people tend not to vote.