Can You Use an iPod Cable for an iPhone 3G?

Whether or not you can use your iPod cable with your iPhone will depend on which iPod you have. More specifically, it will depend on which type of cable you have--USB or firewire.
Different kinds of iPods
There are a variety of iPods that have been on the market for years. Different iPods will connect to your computer as well as charge in different ways. There are two essential types of cables that come with an iPod; firewires and USB 2.0 cords.
The specific differences between the two kinds of cables that iPods use is not essential to know here, but you should be able to tell them apart easily enough upon quick examination.
USB 2.0 Cables
The USB cord that comes with some versions of the iPod, including the 5th generation iPods, have one end that fits into the bottom of the iPod, and another which fits into a computer USB port or a charging adapter for your wall outlets.
The USB 2.0 cord is a common plug that almost all computers today have ports for, as most computer peripherals have these types of plugs. You can identify it by the standard rectangular shape of the metallic connector and a symbol on it that resembles a branching tree near the metallic connector.
This branching tree image is the universal USB symbol.
Firewire Cables
At first glance, the firewire cable looks similar to the USB cord of other iPods. The connection to the iPod itself is the same, while the other end (the end that connects to the computer), is different.
Rather than being simply rectangular in shape, the firewire is more oddly shaped-having a kind of trapezoidal shape rather than a rectangle. The port that it plugs into will not be rectangular either, as a standard USB 2.0 port is.
The best way to distinguish the firewire from the USB cable is the symbol on the plug itself. The USB symbol can be seen on the picture above (the branch-looking symbol), and the symbol of the firewire is a circle with three symbols around it, creating an easily identifiable "Y"-shape as a whole. This symbol is the universal symbol for firewire.
The iPhone
The iPhone uses a USB 2.0 cable to connect to your computer. It also connects to the adapter that allows you to plug it into the wall to charge. You can use this cable to either charge or sync your iPhone.
ipod cables and iPhone cables
If your iPod uses a USB 2.0 cable, you can use that same cable with your iPhone to either charge or to sync it with iTunes. This is because the USB cables used with iPods are interchangeable with the USB cables used with iPhones.
You cannot use the iPod firewire cables to sync the iPhone. Since the firewire and USB cables use different voltages, attempting to charge your iPhone through the iPod firewire cable is not recommended.