Let's cut to the bottom line: In terms of usability, iPhone blew away its two competitors. Its overall score in the usability tests was 4.6 out of 5. The HTC Touch was a distant second at 3.4, and the Nokia N95 scored 3.2.
"Testers were [typically] about twice as fast doing specific tasks on the iPhone, which is pretty remarkable," Thornton said.
Here is a breakdown of how each device scored in the five sometimes-overlapping categories, along with comments from Ballew and Thornton.
Global navigationApple iPhone 5
5 out of 5
HTC Touch 4
4 out of 5
Nokia N95 2.5
2.5 out of 5
Global navigation refers to how simple it is to navigate through the operating system and how easy it is to find and select specific applications. The clear winner in this category was the iPhone. One reason for iPhone's high marks is its simplicity, Ballew noted.
"It has one top-level menu, and it has only one button, which lessens the learning curve," he said.
The HTC Touch did reasonably well, in part because, as a Windows Mobile device, it looks and acts somewhat like desktop Windows, which many people are familiar with. People can choose between standard Windows Mobile navigation and using its touch-screen capabilities.
The Nokia N95, however, suffered from too much complexity, even for basic tasks.
"People had a hard time turning it on," Thornton said. "Only 30% of our sample group could turn it on right away."
Once turned on, navigation was confusing to some users.
"You can access different menus from different locations, which can be disorienting," Ballew said. "And common features are hard to find -- turning the sound down, putting it on vibrate, things like that."