We are not talking about the newly released patches which use a new signal formula. A few people have reported into sites like Gizmodo iFixit and iPhoneHacks that their newer iPhone has a “matted” stainless steel band instead of a shinny one – which could be some kind of non conductive coating.
iFixit exchange their day 1 iPhone with one of the new batch and they verify the new casing is in fact non conductive.
iFixit also suggest how users can find out:
If you got an iPhone in the last few days, check the serial number. If the production week is bigger than 27, try checking the impedance of the metal frame with a multimeter. If you hold the leads about an inch apart, the resistance should be less than one ohm. If it’s substantially higher, you may have a unit with the new coating. (Accuracy of multimeters varies dramatically, but we’d expect a nonconductive coating to have a very high impedance.)
You can find out which week your iPhone was manufactured from the serial number (seen in iTunes summary page). The first two digits of the serial number tells you the factory ID of where it was manufactured and the next three digits (Digits 3-4-5) tells you when it was manufactured.
Example: xx025xxxxxx – the 0 means 2010, and the 25 is the week of 2010 that it was manufactured.
