Four Android phones show the evolution of models using Google's mobile operating system from early days to the present.
T-Mobile G1: The first Android phone
The T-Mobile G1, built by HTC, was the first Android phone. It's slow by modern Android phone standards. In 2008, when it arrived, the Android Market was almost devoid of applications, but now it's improved. So far at least, the G1 isn't available to ordinary folks with the latest version 2.1 of Google's Android operating system.
The Google Ion offers this home screen and two others for housing frequently used applications. I find three screens too confining, but newer phones offer more: five for the Nexus One and seven for the HTC Desire and Incredible with the Sense UI.
The Google Ion, a developer phone, is my mainstay right now. But it's not great: I have to reboot it every few days, and it takes so long to restart that this splash screen now has negative connotations in my mind.
The HTC Desire comes with real hardware buttons on the bottom, a welcome option. Given that it has a touch screen, the "fingermouse" below isn't as useful as it is on phones such as most BlackBerry models, and I actually prefer a trackball for positioning a cursor within a block of text.
The Sense UI of newer HTC Android phones has a nice miniature-screen view to let you flip through different screens. Since you can put miniature applications widgets on each screen, this feature functions like lightweight multitasking.