There is a lesson in the comparative case studies of the Palm Pilot and iPod. Brand intangibles such as music propel critical mass in technology evolution. The "killer app" of the Palm V is managing time and contacts. Useful. Yes, but not enough to move past the die-hard tech geek.
The value of the iPod is that in 5 minutes of opening the box and plugging it in the average consumer is buying music online. They are hunting down that song they rememeber from high school. The songs that complete them. Contacts and calendar items can't do that.
The cell phone has similar attributes. You turn it on and call someone anywhere. It sounds so simple but this is what will drive successful development of applications.
Next for the iPod is likely to be wireless sharing applications to allow for playlist beaming and simultaneous sampling of other peoples playlists via Bluetooth and WiFi. It is the natural evolution of devices. It is also the key ingredient to building effective buzz beyond one consumer affinity.
Maybe we have been using the wrong term of "killer app"? Maybe the new term should be "human app". Applications that are natural extensions of what people desire. Not need...desire.
We expect to see the merging of iPod-like functions with cell phones. This will be the ultimate human device that everyone will want. The needs-based apps don't go away - they just get through better with desire-based apps as the development gateway.