AT&T has had the iPhone since June 2007—that’s right, almost four years. Now Verizon has the iPhone 4 and for the most part they’re the same, but there are differences in specs and performance.

The two versions of the iPhone 4 are virtually identical in appearance, and they both have the same antenna flaw that was reported last July. Those small black dividers in the metal band around the lower part of the phone are insulators that keep the antenna electrically isolated.

When you cover one of those dividers with your hand or finger, though, the antenna is electrically “deformed” and a call may be dropped or signal strength may suffer. To fix the problem, all you do is add an insulated case or wrapper. In other words, don’t touch the antenna.

As for other features, the Verizon iPhone 4 lets you use the phone as a Wi-Fi hotspot. Up to four Wi-Fi enabled laptops or whatever can link up and use the EV-DO data connection to the network. AT&T’s version of the iPhone 4 can’t do that—yet. In any case, it’s a cool feature.

The really big difference between the two phones is the radios. AT&T’s radios use GSM, WCDMA, and HSPA technologies. The Verizon phone uses the CDMA, EV-DO, and Rev. A technologies. That’s a huge difference. Both work well, but they’re totally incompatible. There are differences in performance, too.

Metrico Wireless recently tested the two iPhone 4 versions and reported some amazing disparities. This company tests and evaluates wireless devices for pre-launch and post-launch. Carriers use Metrico to check out phones for their audio, data, streaming video, and location-based information before they are added to the carriers’ product lineups.

The AT&T iPhone experienced double the mean data download speed of the Verizon iPhone. On the other hand, the mean load time for an average Web page was about the same on both devices. Many consumers buy products by speed alone.

I can remember when consumers had to have the fastest PC. “My 2-GHz processor is better than your 1.5-GHz processor,” folks would say. But in reality, hardly anyone could tell the difference between the two unless they were really taxing the processor with games and similar applications.

The same goes for cell phones. As long as response times to your commands are adequate, you’re okay with them. Who really cares or even knows the speed anyway? But the pure speed really helps on big files and video downloads.

“The mobile industry is competing on performance, and anecdotal performance information isn’t good enough to drive management and marketing decisions,” says Rich McNally, vice president of information products at Metrico. “Metrico’s smart-phone program provides carriers and OEMs with an information resource that establishes an objective and scientifically derived user-experience performance baseline.” It’s about time someone did this kind of testing.

The speed difference really comes from AT&T’s faster network. AT&T has more HSPA with fiber backhaul than Verizon has fast EV-DO or rarefied Rev. A networks. Yes, Verizon does have more Long-Term Evolution (LTE) than AT&T at this point, but neither version of the iPhone 4 uses LTE.

Other Metrico test results showed that when the iPhone was mobile, the AT&T iPhone successfully completed about 10% more data download sessions than the Verizon iPhone. The results were the opposite when the iPhones were stationary. The Verizon phone was more consistent uploading data when stationary compared to the AT&T phone, with a 10% better success rate.

Metrico tested a wide range of smart phone against the iPhone 4 models. The iPhone 4 is at or near the top of the list against phones from LG, HTC, Motorola, Sony Ericsson, and Samsung. Check Metrico’s Web site for more details.