No matter how fancy a smartphone is, it's not worth much if it doesn't make decent calls. You may have music, apps, and the Internet, but connecting to a carrier's network and enjoying satisfying audio clarity is much more important.

For much of its life, AT&T's iPhone hasn't received rave reviews as a phone. Many users, particularly those in dense urban areas, have long complained that making a call and keeping it once they're connected could be difficult. Those issues caused a lot of consumers to look to the long-rumored Verizon iPhone as the cure to their reception woes. And now that Big Red's iPhone is finally a reality, we've been able to put it to the test.

Below you'll find voice samples from both iPhones. We used the same process that we're now including in all CNET cell phone reviews. Using the test device, we call a landline phone from the CNET offices and leave a scripted message. We then take the audio from that voice mail and put it in the media player that you see below.

The difference between the two samples is striking. Admittedly, we had a difficult time actually describing that difference, since we're not trained audio engineers. Yet, we can surmise that the Verizon sample is clearer and sharper, but also a bit tinnier and harsher. In contrast, the AT&T sample sounds a bit warmer, but my voice sounds a little softer than it normally is.

Hopefully, this gives you an idea of how much a carrier's network can affect call quality. As you'll listen here, the same device (well, almost the same device) can sound completely different. We've also conducted extensive testing of signal strength and data speeds, so we invite you to check out these results as well. And, of course, please see our Verizon iPhone 4 review for the full analysis of a handset that a good number of people have been eagerly awaiting for years.