These are the 3g model numbers that will appear in "model" under settings, about:
MB046 A1241 iPhone 3G 8GB Black
MB489 A1241 iPhone 3G 8GB Black
MB048 A1241 iPhone 3G 16GB Black
MB496 A1241 iPhone 3G 16GB Black
MB499 A1241 iPhone 3G 16GB White
MB501 A1241 iPhone 3G 16GB White
MB632 A1241 iPhone 3G 16GB White
These are the 3gs model numbers:
MB715 A1303 iPhone 3GS 16GB Black
MB735 A1303 iPhone 3GS 16GB Black
MB716 A1303 iPhone 3GS 16GB White
MB736 A1303 iPhone 3GS 16GB White
MB717 A1303 iPhone 3GS 32GB Black
MB737 A1303 iPhone 3GS 32GB Black
MC133 A1303 iPhone 3GS 32GB Black
MB718 A1303 iPhone 3GS 32GB White
MB738 A1303 iPhone 3GS 32GB White