The yellowing on my 16GB iPhone 4 has gotten even worse now that I actually took it outside for the day using it in the sun and shade (temps were about 90F today). Using a few apps at a time the device did heat up qucikly. Used the flashlight app and the yellow pea sized dot in the upper left corner has now started to bleed downwards in a lighter shade of yellow all the way to the bottom left corner! Also, a new yellow smaller dot has formed in the mid/upper right mid-section of the phone and is also started to bleed downwards in a lighter shade. It almost looks like a streak. Took the phone indoor in the AC for an hour to cool down and the streaks went away , but could still see the yellowish dots. Then, took the phone back outside for an hour or so and the streaks came back and were much more visible. This thing is getting worse the warmer it gets! It almost looks like smeared residue now once it gets really hot. Makes me wonder what type of petro-chemical I'm putting near my face. I love the phone, and hopefully will get a new one at the store tomorrow.