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The present hype is around Third-Generation (3G) phones, which will provide most of the advanced services planned until at least 2010. But it's worth looking at the other generations and the features they offer.
First-generation phones are analog, meaning that they send information as a continuously varying waveform. They can only be used for voice and have highly variable call quality, thanks to interference. Another serious disadvantage is that they are very insecure; snoopers can listen in on calls with a simple radio tuner, or can even charge calls to another person's account. The first-generation AMPS standard is still popular in the U.S., but is seldom used elsewhere.