Reports started surfacing today that Apple may have quietly revised the iPhone 4 to add a nonconductive coating to the metal band on the sides of the phone. This would fix the sudden signal drop from electrically bridging the antennas by touching the band in the bottom-left corner with your hand.
We got an independent report of a similarly updated phone from a member of our community, so we decided to investigate. We exchanged one of our units (that had been experiencing unrelated problems with its Bluetooth connection) to see Apple has changed the manufacturing process since their initial production run.
The serial number on the unit tells you the manufacture date; our original phone was manufactured in mid-June (week 25). The replacement unit we got was made in early-July (week 27), apparently too soon for a manufacturing change.
The serial number also identifies which factory it was made in. (We don’t have a mapping of numbers to physical factories, but we can tell if two phones came from the same plant.) Apple has always done this, and we’ve occasionally had fun comparing Macs to see if they were birthed in the same place. A fun aside: I once had a Mac made in Apple’s Elk Grove, California factory. This information may be useful if Apple is rolling the production change out to their factories one at a time.
The iPhone 4 serial number is easy to decode! It’s in this format:
aa = Factory and Machine ID
b = Year
cc = Production Week
ddd = Unique Identifier
ee = Colour
f = size
Our serial numbers:
85025xxxA4S (16GB unit we took apart)
86025xxxA4T (32GB test unit)
86027xxxA4T (32GB replacement)
Apple has so many iPhones out in the field that it’s very hard to get a feel for what’s going on. They may have just switched to their new process at one of their factories, or they may be rolling it out slowly, or this may be an internet myth. The only way to find out is to check a number of units that have just shipped from the factory.
We need your help! 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.)