RapidRepair has opened their brand new iPhones so you could have a look at what is inside the brand new iPhone. There is complete analysis of the guts of the new iPhone 3GS and of course the old iPhone 3G.
The motherboards differ in these given that iPhone 3GS having a faster processor and built in video and the Compass.
Following information gives some details of the iPhone 3GS;
iPhone 3G S system board is shown on the left, right board is iPhone 3G.
CPU - Samsung
NAND Flash Memory - Toshiba TH58NVG702ELA89
System Memory - 337S3754
Infineon - 36MY1EE
You can get all the gory details at RapidRepair