Update: As pointed out below, our original analysis here did not highlight the difference between the subsidized pricing (what consumers pay with a 2-year contract) and the much higher unsubsidized price (what carriers pay Apple for each phone). The unsubsidized price of the 16 GB iPhone 4 is not disclosed by Apple but is likely to be about $599, the same as the original pricing on the 3GS. iSuppli's pricing methodology has been criticized in the past for inaccuracy. We apologize for the error.
iSuppli has done its usual thing with the16GB iPhone 4's components, calculating the raw cost of each of them, and the total comes to: US$187.51. The most expensive thing in the phone is the retina display screen, which is supposedly running Apple $28.50 per unit. The A4 processor adds $10.75 to the unit price, and the gyroscope adds $2.60, as compared to the accelerometer's estimated 65 cent cost.
You may remember that the iPhone 3GS was estimated to have components costing $179 last year at release -- the price on those parts has dropped to $134, even though the phone itself is being sold at $99
(but Apple is probably just selling off inventory -- an unsold phone isn't worth anything to them). [Since carrier subsidies still hold for the 3GS, it's presumably still priced well above that number for the transaction between Apple and AT&T. –Ed.]
The 3GS was also $199 at launch [presumably $599 unsubsidized], which means that Apple is making $10 less per phone with the iPhone 4, but maybe they're making up the costs elsewhere, maybe in advertising or R&D. Of course, these are all estimates -- there are all sorts of other factors going into this cost equation, both internally at Apple and in the manufacturing industry. But iSuppli has been doing this for a while now, and if they say the screen is the priciest component in your new iPhone, they're probably right.