It’s what a lot of people have been wondering – how does the iPhone 4 perform on Verizon Wireless’ network compared to AT&T’s network? Metrico Wireless put the phones to the test, and found that – drum roll, please – it depends.

The AT&T iPhone experienced double the mean data download speed of the Verizon iPhone, but the mean load time for an average Web page was about the same on both devices. When the iPhone is mobile, the AT&T iPhone successfully completed around 10 percent more data download sessions than the Verizon iPhone, according to Metrico. The results were opposite when the iPhones were stationary; the Verizon iPhone was more consistent uploading data when stationary, with a 10 percent better success rate.

Rich McNally, vice president, Information Products at Metrico, says the tests were conducted, with off-the-shelf devices that Metrico bought, in five markets: Seattle, New York City, Baltimore-Washington, D.C., Chicago and Dallas. Now for the big question that McNally is getting asked a lot lately: Did the devices have the bumpers on them that Apple advises be used to combat that “antennagate” problem? No, he says. When Metrico testers conduct their tests, they’re trying to get many, many samples and they’re not always holding the phone; it’s in a cradle.

The iPhone 4 is the latest of more than 80 smartphones evaluated to date as part of Metrico’s Smartphone Mobile Experience (M.E.) evaluation program, which evaluates the performance of commercially available smartphones sold by Tier 1 U.S. carriers. Separately, Metrico also conducts tests on devices before they’re released into the market, and those results are held in confidence for clients.

As part of Metrico’s Smartphone M.E. program, the company compared the AT&T iPhone to 22 other AT&T smartphones. When compared to other AT&T smartphones:

• The AT&T iPhone ranks near the top on data download and upload speed, with comparable performance to the Sony Ericsson Xperia, the LG Quantum and the HTC Surround.

• The AT&T iPhone ranks below average in Bluetooth speech quality behind top rated performers like the Blackberry Torch and Blackberry Curve.

• The AT&T iPhone ranks in the middle of the pack on call performance behind top-rated performers like the Samsung Captivate and the HTC Aria.

When compared to 17 other Verizon smartphones:

• The Verizon iPhone ranks near the top in noise cancelling performance, joining the likes of the Motorola Droid X and the LG Ally.

• The iPhone ranks below average in data download speed relative to other Verizon smartphones like the HTC Incredible.

• The iPhone is comparable to the Verizon average in speech quality, behind top performers like the LG Fathom.

In its special report, Metrico measured data download speed, Web browsing, call performance and voice quality on both live and simulated mobile networks to obtain statistically valid metrics on the real-world performance of both versions of the iPhone. To collect performance evaluation data for the report, Metrico performed over 10,000 Web page downloads, ran more than 2,000 data download/upload tests and made nearly 4,000 voice calls.