Making calls was the killer app for Nokia brick phones in the late 1990s.
The killer app for the first generation of smartphones (Windows Mobile, Blackberry, etc.) was email and calendar.
The killer app for iPhone and Android was the capacitative touchscreen combined with the ability to run 3rd party apps (yes, I'm aware there was an extremely brief moment in the history of the original iPhone where Apple opposed this), and 3G mobile internet (yes, again, I realize this came a year after the initial iPhone release). Mobile web browsers and Maps/GPS got the party started.
What?
Making calls was the killer app for Nokia brick phones in the late 1990s.
The killer app for the first generation of smartphones (Windows Mobile, Blackberry, etc.) was email and calendar.
The killer app for iPhone and Android was the capacitative touchscreen combined with the ability to run 3rd party apps (yes, I'm aware there was an extremely brief moment in the history of the original iPhone where Apple opposed this), and 3G mobile internet (yes, again, I realize this came a year after the initial iPhone release). Mobile web browsers and Maps/GPS got the party started.