Seems the strings to set 3G preferences exist in the code of iPhone 2.0 Beta 5, but the GUI screen that was rumored to surface it was a mock-up, a photoshop, a con-job, a bamboozle.
The process used to determine that the screen was less "shot" and more "not" is rather involved and -- quite frankly -- convoluted but the bottom line remains:
We're getting a 3G iPhone. That 3G iPhone will have settings. We, as yet, have no idea what form those settings will take.
Now bring on the next rumor!