I had a t-mobile Sidekick the first week it was out, and I loved it, though it was too big. Mine died a couple of years ago, and it would have been expensive to replace, so I didn't...never was my main phone. It pleasantly surprised me on a routine basis, though.
I thought that maybe the new Dash (a Windows Mobile device made by HTC) would satisfy the "one phone that does everything" problem. And it's thin enough to go in your pocket, even though you worry about scratching the screen. The full-sized Blackberry and Palm can't do that.
But man, the software. After 24 hours of wrestling, I think I can articulate what I think about Windows Mobile now. (This is the "smartphone edition" - a blackberry-esque re-simplification of Windows Mobile.)
It's not that it can't do everything, or that it's hard to figure out - it's not. It's that it's just no fun. While the phone itself is fast, the UI just takes 3 times as long to accomplish most tasks as it does on a Nokia or a Samsung or even a Sidekick, and the breadth isn't -- worth it.
This means that the t-mobile Dash doesn't have that elusive pleasant feeling of surprising you by making a set of things easy - the way that a Series 40 Nokia is a good phone, and a Sidekick is a good IM client, and a Blackberry is good at email, and an iPod is good at being an iPod.
I had an old college friend visiting yesterday, and he asked if maybe mass customization wasn't the path for handheld devices - you buy a device with software and hardware that is customized and designed perfectly for you. I think this is a brilliant idea and one that pretty much has to happen. All tasks just aren't equally important to all people. This is apparently the mistake that some of the popular Symbian OSes make, and certainly that this Windows Mobile phone makes.
Meanwhile I have a phone that runs applications that I have to shutdown sometimes using Task Manager, and writing a new text message is just that many steps harder, and somehow I can spend hours doing nothing more than I could using a more focused device.
And the very nice Google Java apps display no fewer than 3 warnings each time you run them (this is after you open "Java" in the "Applications" folder under the "Start" menu).
Overall, it has a beautiful screen and fits in my pocket, but it was designed by committee, and so it does a whole lot of things in a mediocre way. Devices made by small teams have obvious limitations, but a person who is actually allowed to craft the perfect experience makes a thing that is wonderfully better at doing something than something that is generic.
The problem in the technology world is that this piece of top-level design: the insight that distinguishes the main screen of an iPod from the main screen of a Blackberry is the lowest level in the technology stack (e.g., the application launcher, the global navigation), and it is the thing that software engineers like doing the least, and so it is the least flexible and customizable today.
But I am convinced that there needs to be some serious work on this to make devices that work for people.