Background: FM Radio

For a quick explanation, let's first look at a familiar radio scenario. FM radio stations are all assigned frequencies (like 95.6, 102.1, and so on). Stations can have the same frequency as long as there is sufficient distance between them. Have you ever been driving along, listening to your FM radio, when two stations seem to be fighting for the same frequency and you hear both? This happens when you're driving through an area where two stations using the same (or close to the same) frequencies overlap slightly.

Codes help avoid confusion

Usually, cellular networks work in a similar way. When you call someone, you're assigned a channel for the duration of your call. When you send data over GPRS, your phone looks for an empty channel to use. With WCDMA, voice calls and data connections are each assigned codes, not specific frequency channels - hence the term "Code-Division Multiple Access." The device on the receiving end knows the proper code, and automatically filters out any data that isn't stamped with it. This method frees a lot of space on the network that otherwise wouldn't be available, and it adds security.

Wideband makes data flow faster

Imagine pouring water out of a bottle. If the bottleneck is narrow, you may have lots of water to pour but it's only going to go as fast as the narrow opening will let it. This is where the "Wideband" part of WCDMA comes in: it becomes more like pouring water out of a vase. It's not that the individual water molecules (or bits of data) move any faster, but much more can be transferred at any given time.

That's a very simplified look at the principles behind WCDMA.

What if WCDMA isn't covered?

If your phone uses WCDMA and you enter an area where the networks don't yet support it, the phone are designed to automatically switch to using GPRS or EDGE, whichever is available. This is built in to Nokia models - they're called multimode WCDMA/EDGE terminals.