Newer iPhone USB cables tear at the ends, unlike old style iPhone USB cable
http://i.imgur.com/KjGUx.jpg (USB ends)
http://i.imgur.com/ueJ9m.jpg (30-pin connector ends)
For the USB ends, the older style had a plastic cylindrical section covering the joint where the cable and USB head met. The same goes for the 30-pin connector end.
Macbook Pro (silver), Mac OS X (10.6.2), iPhone 2G