Third-party stuff: Developers are just beginning to hop on the Android bandwagon. The iPhone-like Market service lets you download apps directly to the phone from Google; unlike with the iPhone, you can also snag programs from third-party merchants such as Handango.

Bottom line: Android's potential is gigantic, especially if it winds up on scads of phones. On the G1, it's a promising work in progress.

RIM BlackBerry OS

What it is: This software powers RIM's BlackBerry smart phones, including the Curve, Pearl, and 8800, as well as the new Bold and Storm models.

How it works: The basic concepts behind the BlackBerry interface have changed remarkably little in a decade. And why should they? In its own way, the BlackBerry interface is just as logical and consistent as the iPhone's: On most models you perform almost every function in every application with a trackball, a Menu button, and a button that lets you back out to the previous screen.

Master those three actions, and you can whip around the OS with extreme speed. (I haven't tried the Storm, which replaces the standard BlackBerry controls with an iPhone-style touch screen.)

How it looks: The BlackBerry OS is fairly mundane and text-centric, although recent models such as the Bold dress it up with crisper fonts and slicker icons.

Built-in applications: The BlackBerry's e-mail and calendaring applications still set the standard for efficient design and reliable real-time connectivity with widely used messaging systems such as Microsoft Exchange.

The Bold introduces a much-improved new browser that rivals iPhone OS and Android in its ability to display sites the way their designers intended; its music and video apps are serviceable enough but still secondary to the productivity tools.

Third-party stuff: Once upon a time, users didn't have many BlackBerry programs to choose from, but recently the market has boomed--thousands, from productivity apps to games, are available now. Windows Mobile and S60 have even more bountiful selections, though.

Currently BlackBerry has no over-the-air storefront comparable to Apple's App Store or Android Market. RIM's BlackBerry storefront is expected to launch in March 2009.

Bottom line: The BlackBerry OS is an old dog, but a smart one--and one that's proving itself capable of learning new tricks.

Next: Microsoft Windows Mobile and Nokia S60 3rd Edition on Symbian

Microsoft Windows Mobile

What it is: As its name makes clear, this is Microsoft's mobile edition of Windows. Version 6.1 ships on a dozen phones from manufacturers such as HTC (with its Touch Diamond), Motorola, Palm, and Samsung.