Harrry McCracken ( https://twitter.com/harrymccracken ) points-out that that there were handheld devices that look like tablets and Smartphones in the title sequence of The Jetsons:
http://techland.time.com/2012/09/23/the-jetsons-turns-fifty/
The Jetsons Turns Fifty: How the Future Looked in 1962 [TIME.com]
