Tried it, can't reproduce it. Or any of the other "sure-fire" configurations people have claimed.

If it really is a hardware issue, it's probably due to a defect in some batches of phones. But for now I'm sticking to the most likely explanation, which is just that cell phones are finicky little beasties and people are quick to spot patterns where none exist.

This video shows one iPhone calling another when the phones are within a few inches, as close as 1 inch apart. It's frankly amazing that the call completes, and doesn't drop more often. This video isn't particularly reliable evidence of a problem. My own experience indicates that there is a high probability of serious radio frequency interference between two cell phones that are closer than about 10 or 12 inches to each other. Older phone models often had trouble within about 3 feet of another cell phone.