Gene Munster reports via MacRumors that 34% of high school students own an iPhone:

In our most recent survey the percentage of teens that own an iPhone came in at 34%, up from 23% in the Fall and 17% last Spring. We believe the meaningful uptick in iPhone ownership among teens may be driven by the cheaper $49 iPhone 3GS (in some cases free). Interest in purchasing an iPhone in the next 6 months rose to 40% (another all-time high vs. our previous surveys). Purchase intent was at 38% in our last survey in the Fall.

It also reports that tablet ownership is around the 34% mark also with 70% of those being iPads.

With the new iPad just launched and a lower $399 price point for the iPad 2, expect these numbers to increase.