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I noticed the yellow splotches the afternoon ofmJune 24. I called Apple and was told adhesive needs to dry, give it a few days. Later that evening I realized it was reappeared when the phone got hot. The adhesive story is a lie.

I called today and said I wanted an advanced replacement and she could take my credit card. There was no argument. When I asked of it was new in box and she said no, a refurbished phone. I said that was not cool since I waited three and a half hours just four days ago for a new phone. She then said she thought it was a 3GS and said it is new in box. Before I hung up I confirmed it was a new in box iPhone and she said yes.

It is only a credit card hold for an advance replacement. As long as you return it on time there is no chrage to your credit card. It works fine with all the splotches, just use that instead of sending the phone in and then they send you a replacement. Why bother with a loaner phone?

It's not a lie, when it gets warms it seems the adhesive story is not a lie.
When it gets warm it seems the adhesive is coming unglued again, that is why its showing up. Think about it like this, put a piece of scotch tape on your hand, then put your hand over some steam (to warm it up), what happens to the tape?

It starts to come unglued, that is what is happening with the adhesive. They probably used some cheap stuff that is coming unglued when it gets too warm
 
Is the yellow discoloration present all the time even when the device is cool? I noticed mine immediately after restoring for about an hour so the devce was pretty warm/hot. It completely disappears after it has cooled down, but seems to reappear when it gets warm again; although it seems more faint now.
 
Update from OP

Earlier this week my problem had not gone away. I went to Apple store on Tuesday and showed them the phone. They put me on the list to get a replacement, which arrived Thursday. It was a painless swap, and now I'm good to go. New phone is week 26 and has NO splotching. Oddly enough I was able to show them the best of both worlds. When I went in on Tuesday, it was actually pretty faint. I feared they may not see it well enough to take me seriously. They were actually very cool about it, though. On Thursday when I picked up, the problem was also the worst it has ever been... which contradicts the whole "it will go away" theory.

My advice: If you still have splotches, take it in and get it swapped out. Even if you have to sit on a waiting list for a few days, you might as well get that process started.
 
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