My iPhone has the occasional lock up, but almost every single time it's a result of a third party app screwing up. But usually these problems are pretty visible, and the third parties are quick to have a patch.

I have a bit of beef with my phone, but the pros far out do the cons. It is by far the most fun and intuitive mobile device I've used. The biggest advantages are in how much you can do without having to go through the extra steps that exist in doing the same thing with other devices (controlling music on PC, downloading directly to the phone, etc.).

Also, Windows Mobile is a piece of junk, and there is no getting around that. Take THAT!

; )