GPS. The US government quit "fuzzing" GPS 2000-05-01, and GPS receivers were somewhat expensive until well after that. Games, email, texting, etc, are cool, but until you can keep time accurately, and use location services, smart phones are just toys.

Transcript: https://www.npr.org/transcripts/nx-s1-5872785

This headline isn't great. It's an interview with Tony Fadell who invented the iPod, iPhone, and Nest thermostat. Before the iPod, Fadell worked at failed PDA maker General Magic. The interview doesn't get into other 90s attempts like the IBM Simon, Palm Pilot, or Apple Newton.

There's also a documentary about General Magic: https://www.youtube.com/watch?v=JQymn5flcek