Spotted the iPhone on The colbert Report. during a routine parodying Twitter, Colbert used a 2G while Jeff Goldblum had a 3G. I guess that even celebs must have to wait for upgrades!
Some people just don't care that much, and most celebs don't have time to browse the web while walking, cause they are always going from point to point to point and there is always WiFi and computers there the 3G speed isn't that important for them.
Oh and I doubt colbert even uses an iPhone. Like most celebrities I'm sure he has a blackberry. Most celebs have old blackberry curves. No idea why.