Got my replacement iPhone 3G 8GB the other day..
It was an out of warranty iPhone, and they completely replaced it for free...
Here is what happened..
I purchased an iPhone second hand for £210, pretty good price.. Minor scuff marks on it.. (We have 2 other iPhones, so was just a backup one. Due to the price i had to snap it up)
After a few days i noticed a small scratch by the dock, very hard to notice so i wasn't to annoyed.. But i researched how to replace the back due to this problem and noticed many other iPhone users had the crack occur, also had their phones replaced in warranty.
So i rang up Applecare, i was very polite and just put across that other people experienced this problem and got replacements in warranty..
Argued that if these phones are being sold on 24 month contracts, why aren't they built to last within that 24 month period or at least replaced if this defect happened..
After being escalated to someone else, a very nice chap asked me for a picture of the crack. I also sent a picture of the phones condition to show no impact damage was present.
Next day i receive a phone call, notes had been added to my account to have a full replacement issued.. Quick pop down to an apple store (Although had to go twice as notes didnt pop up correctly on first visit)... Full replacement given to me :)
Below is some paperwork, shows what they wrote on the form.. Also below is picture i took of the crack and sent to the Applecare guy.
Goodluck to anyone trying this.