Some good stats on iPhone from Nielson. They don't seem to mention the source, so I guess it could be either surveys or Telephia bill-scraping.
Here are the numbers:
As of April 2009, the number of iPhone users in the U.S. was 6.4 million (up from 2.1 million a year prior).
Forty-percent of iPhone subscribers have household incomes of $100,000 or more, compared with 19% for all subscribers.
Age ranges of iPhone subscribers:
And they report that 75% of iPhone subscribers download apps.
That last number is surprising. Does that mean the other 25% don't have iTunes accounts? Are they not interested in apps? Or are do they have jailbroken devices?
Update: I forgot to mention the iPod Touch. AdMob estimates that there were 22.5 million iPhone and iPod Touch devices in the US (75% of 30 million) in March 2009. If both Neilson and Admob are correct (and you disregard the 3 month time gap), that would mean 16.1 million iPod Touch devices in the US.