Interestingly the now "base" model 16gb version runs almost the same build cost as last years 3G. And although you would think for this reason and obvious "at first glance" conclusions that most internals have been kept from the previous 3G....that is actually not the case.
The entry-level, 16Gbyte version of Apple Inc.ís new iPhone 3G S carries a BOM cost of $172.46 and a manufacturing expense of $6.50, for a total of $178.96," said Andrew Rassweiler, director and principal analyst, teardown services, for iSuppli. "This is slightly higher than iSuppliís estimate of $174.33 for the original 8Gbyte iPhone 3G based on pricing in July 2008. Although the retail price of the 16Gbyte iPhone 3G S is $199, the same as for the 8Gbyte version of the original iPhone 3G, the actual price of the phone paid by the service provider is considerably higher, reflecting the common wireless industry practice of subsidizing the upfront cost of a mobile phone and then making a profit on subscriptions.
You also have to remember Apple's agreement with AT&T provides Apple with a tidy profit margin including dipping into service plan income.
See the full iSuppli article here