I tried to show a friend an HD video on youtube on my iPhone4. However, the videos came up on low quality (I was on 3g). To check if it was my phone, I had a coworker pull up the same video on his 3GS and it came up low quality, so that eliminated the possiblity of the issue being my phone. I then had another coworker pull up the same exact video up on his HTC EVO on 3G and it came up on HD. We then jumped on WiFi and my iPhone4 pulled up the video in HD. I don't recall AT&T dumbing down HD YouTube streams on 3G. I remember pulling a video up on my 3GS on the 3G network not too long ago. If this is the case, this would solidify the fact that AT&T sucks big time.