So, here is the interesting thing. iPhone 3Gs’ that were pre ordered they have an FCC ID of BCGA1303A, however iPhones that you buy now have the ID BCGA1303B.
And when I look up both models in the FCC database, I cannot spot any differences between them when comparing documents! (Only thing that I thought was sort of weird was that the testing reports for the WLAN/WiFi was done for one device, while the WWAN/cellular radio testing was published for the other, even though both devices were certified for all the frequencies covered by both WLAN and WWAN radios. Huh.)
I’m sure that what we have here is NOT two different revisions of the device, A and B, with B being released at a later date to either correct engineering in hardware or reduce cost of manufacture. The reason I say this is because both devices were submitted for testing to the FCC on the same day, AND both devices were approved on the same day! (And it was a 16GB white phone in the pictures, and if you look closely at the external pictures, the only one that differs between the two is in fact the shot of the back, and both phones clearly show an FCC ID on themselves different from the other.) Not only that, but it is clear that both devices are being manufactured concurrently and distributed simultaneously within the US.
Neither the original iPhone nor the iPhone 3G were registered under multiple different FCC ID numbers. So why would Apple have the 3GS approved twice, and go through the trouble of manufacturing 2 different plastic backs for all 4 models (16GB and 32GB black and white, A and B; so 8 total different pieces of plastic that have to be stocked)?
I agree with the authors speculation that it may be a retooled model to reduce production costs, but kinda interesting how there are two ID’s for the 3Gs.