Notification light built into the trackball with customizable colors depending on the app
Back plate came off, replaceable battery
Small and a one handed wonder, the trackball kept my fingers off the screen
It was a replacement for my jail broken iPhone OG, such a better interface for me than the iPhones and it had very basic multitasking when the other guys could only do one app at a time
For real, you sold me on that trackball. That sounds like the coolest feature a phone could have, right down to the multi-color led built in beneath it. I really really hope we see a return to something like that! Touch screens are very useful and have their place but physical buttons/controls are usually preferred when done properly. Here's a pic of the Nexus 1, that trackball indeed appears to be cool as fuck:
Oh hey, it's my 2nd smartphone ever. How nostalgic! This phone was built like an absolute tank. It really was a great little phone.
That said, the problem with physical controls is that you either need a larger device or smaller screen to accommodate them. For most people, the tradeoff just isn't worth it.
For a while, I bemoaned the loss of the physical button bar. Having four (!) indicator lights was really useful to boot. Now I happily use gestures with no looking back.
Would be nice to still see some phones offer this for those who want them, though.
I thought the digital trackball of the HTC Incredible was cool as shit. It was my favorite phone and I would still be using it today (not as a phone) if it didn't have a restart bug that HTC refused to acknowledge.