Third-party stuff: Thanks to Apple's hugely influential App Store, the iPhone has gone from having no third-party apps to having tens of thousands of them--many of which are free--in less than a year. The best ones, such as Facebook and the Evernote note-taker, are outstanding. But the limitations that Apple imposes on third-party apps--they can't run in the background or access data other than their own--put major obstacles in the way of everything from instant messengers to office suites. And Apple, the sole distributor of iPhone software, has declined to make available some useful applications that developers have submitted.
Bottom line: Despite the strides made by Android and WebOS, iPhone OS remains the most enjoyable and intuitive phone operating system in existence. And version 3.0 promises to add many of the advanced features it needs to prevent other competitors from racing past it.
What it is: The Android phone OS is an ambitious open-source platform that Google invites companies to customize to their liking for an array of handsets. So far, however, it's available on just one model in the United States, the T-Mobile G1. However, another 18 Android phones are expected by year's end, and expectations for its long-term success remain high.
How it works: On the G1 and its follow-up, the G2 (due in July), Android's interface feels like an iPhone/BlackBerry mashup--much of it uses the touchscreen, but you also get a trackball and Menu, Home, and Back buttons. The highly customizable Android desktop is reminiscent of those in desktop OSs like Windows Vista and OS X Leopard. You can arrange shortcuts as you like and install widgets such as clocks and search fields. Overall, Android compares well to older platforms, though it isn't as effortless as iPhone OS.
How it looks: Android isn't an aesthetic masterpiece like iPhone OS, but it's clean and appealing, and it makes good use of the high-resolution screens on the G1 and its successor.
Built-in applications: They're tightly integrated with Google services such as Gmail and Google Calendar--and when you turn on the phone for the first time, the first thing you do is give it your Google account info (which is fine as long as you don't depend on alternatives such as Microsoft Exchange). Android's browser lacks the iPhone's multitouch navigation but is otherwise a close rival. Its best music feature is the ability to download DRM-free songs from Amazon. The only videos it can play are YouTube clips, alas.
Third-party stuff: Android hasn't taken off as an app platfom as quickly as the iPhone OS did, but its iPhone-like Market store is rapidly filling up with good stuff, including intriguing apps (such as the Glympse location-sharing service) that aren't yet available on the iPhone. As more Android phones appear, more developers are likely to get excited about writing iPhone-style apps for it.
Bottom line: Android remains a promising work in progress, but its current incarnation is less inventive and elegant than either iPhone OS or WebOS.