I tend to like my Treo650 only to say that I have never tried a Blackberry(yet). My treo does the things I need it to do, but not some of the things I would LIKE it to do. Its Palm so I have to take it for that. It does email ok, using versamail. It will check my email accounts every 15 mins. The calander is just ok, needed a plugin to get it to where I wanted it. As I sit here and think about it, the software that came on/with the Treo is pretty basic.
To get it to where I liked it I had to buy and download A LOT of 3rd party software. There is a lot out there, just wasnt ready out of the box for me.
Another downside to the Treo is that it is easy to break. I have had mine replaced 3 times. Thank God Sprint offers insurance. All in all though I still have it and use it everyday.