What happens when real antenna engineers measure the performance of the iPhone 4’s antenna under different grip conditions? They find that it really needs a bumper:

We can make several interesting observations.

1) Gripping the Naked iPhone 4 certainly had a strong negative effect on the data rates, both upload and download.

2) The effect of the grips on the iPhone 3G is much smaller. But, the Full-Grip still reduces the data rate on upload.

3) Use of the Apple “Bumpers” has a very positive effect on performance. It mitigates much of the effect of the grips at our signal strength level.

4) The iPhone 4 data rates still beat the iPhone 3G data rates under all grip conditions.

5) There was a large spread in the data during the Full-Grip, in both upload and download. This highlights the sensitivity of the antenna design to direct contact by the hand.

In plain terms, the iPhone 4 SmartModule becomes a SmartPhone with the Bumpers.

Interestingly, even without a bumper, the iPhone 4 is still better than the iPhone 3G under all test conditions, but you’ve got to watch out for the throttling.