The Treo 600 was amazing at the time (2003). A little buggy (I used one for a whole service contract), but for its time a tremendous touchscreen device. I "upgraded" to a Treo 700p, which is a 600 with curved keys, a little more screen res, and more memory. Same size, weight and thickness as a 600, though. (This is bad; compare the ipod over the same years). Also a buggy piece of crap, plagued with freezes, sync difficulties, and outright failures. After Palm tried to fix these problems with a firmware update, they trashed their data connectivity for four months in 2007. And when you called them for service they lied about it, saying there was "no known issue." This was demonstrably not true; every Palm message board was howling about it. Fortunately for me Verizon has good customer service; after they sent me 5 700ps they sent me a working 650 until Palm fixed the non-problem firmware. Even now they can do no better than the centro, which is a slightly smaller 5 year old tech phone.
Don't even get me started on the software. The best palm os device I ever had was a Sony Clie, 6 or 7 years ago, and it had the same software, without the kludged and buggy phone added on. The browser "blazer" is horrible.
The problem? It has to be management. No improvements in the hardware or software since 2002. The only thing they tried to innovate with was the silly "fooleo," (in their only wise move of the last 5 years) which they canceled. Their inaction is truly inexplicable. They owned the PDA market and had a huge head start on the smartphone business and they BLEW it.