I just got an email regarding my advanced replacement phone, and it says my new's phone serial number is going to start with a J. What does the J mean? I've never seen a J in a serial number before.
The J designation means that it was personally autographed by Steve Jobs. You just have to tear it apart completely to see the signature between the silver layer of the LCD and the digitizer.
As long as it does not say 5K, your golden. I went through 3 5K replacements, I finally sold my phone on eBay, then used the money to buy a brand new 4. My new one starts with 6Q