iPhone will not show up in iTunes when I plug in USB 3G

I am not able to sync my new iphone 3G S when I plug it into my computer. My old iphone that I did the latest update has the same problem. They will not even chirp or start charging when I plug them in. My shuffle will show up, sync and charge, no problem so I know that the USB ports are working properly. My phones will only charge on wall outlet adaptor. Tried two different apple iphone cables. Could this be a bug or am I doing something wrong?
MacBook Pro iPhone 3G S Mac OS X (10.4.7)