My local Best Buy interpreted the eligability to be those who bought the iPhone 4 at Best Buy or anyone who is a Reward Zone member, regardless of where you bought the phone. I bought mine from AT&T but since I am a Reward Zone member they gave me a FIX4 and installed it for free.
One thing to note is that the section that covers the lower left (i.e the problem area) was slightly too long so it had to be trimmed. Before trimming, the strip either covered part of the volume down botton or partially covered the speaker hole. It was clear that the extra length was not due to stretching the skin. I'd be interested to hear if others have experience the same issue or if there is just bad batch of FIX4 shields.
The local Best Buy told me it was for people who bought the iPhone 4 there until the guy re-read it and agreed it was for RZ members OR purchasers.
I had them install it just in case and 2 of the kits were cut too long but the third one was way better. It comes just to the edge of the actual speaker but it's still better than the first two that went clear over the whole speaker.