Brief History of handheld devices - tablets, PDAs and smart phones:

1967 -  E.A. Johnson at the Royal Radar Establishment, Malvern, UK publishes
        a description of capacitive touch screen technology.
1968 - Alan Kay proposes a portable personal computing tablet, the Dynabook
1972 - Pocket calculator Sinclare, TI, HP
1972 - Danish electronics engineer Bent Stumpe produces prototype capacitance touchscreen.
1974 - Sam Hurst at Elographics produces resistive touch-screens.
1982 - First portable cell phones were big and clunky
1983 -  Hewlett-Packard introduced the HP-150, a home computer with touch screen technology,
        using  grid of infrared beams across the front of the monitor. 
1982 - Grid Compass laptop with a screen supporting 80x24 characters of text. $8150
       Has an full screen text editor, worksheet, database, plot, BASIC and database.
1983 - Radio Shack introduces the TRS-80 Model 100 laptop for $1,099
        8 line x 40 character LCD with 240 by 64 pixel addressable graphics.
        It has text (notes), address and calendar applications and BASIC.
        Becomes the standard for field news/sports reporters
1986 - Psion introduces the Organizer II a pocket computer with a diary and alarm clock,
    It also had end-user programmability and was used for commercial applications.
1988 - Compaq SLT/286 with DOS and the first VGA screen on a laptop
1990 - Wide-area paging introduced and over 22 million pagers were in use.
       By 1994, there were over 61 million pagers in use.
1993 - Apple introduces the Newton, a PDA (personal digital assistant) with
      notes, a calendar, to-do list, address book and a touch sensitive screen
      with handwriting recognition which didn't work very well.
1996 - Jeff Hawkins, Donna Dubinsky, and Ed Colligan invent the palm pilot,
    a PDA with a touch sensitive screen and a shorthand handwriting recognition, graffiti. 
    The palmOS (Palmpilot, Handspring, Treo phone) grows to 14 Million users by 2009.
1999 - Microsoft introduces a tablet PC with no success.
1999 - 2005 Fingerworks develops multi-touch technologies
2001 - The handspring Treo 180 combined the Palm OS with a phone.
2002 - RIM introduces the  BlackBerry 5810, combining email with a phone
       and a small QWERTY keyboard.  Grows to 20 M users by 2010.
2002 - Sanyo and Sprint debuted the Sanyo SCP-5300 PCS phone, with a built-in camera.
2005 - Apple acquires Fingerworks multi-touch technologies.
2007 - Apple releases the iPhone with iOS. As of July. 2011 125 million sold.
       Amazon releases the Kindle e-reader
       Barnes and Noble releases the nook e-reader
2008 -  HTC Dream the first phone with Google's android operating system released.
       By the end of 2011 android was installed on 130 million devices.
2009 - Smartphones (combines features of a PDA and email with a phone) take off.
2010 - Apple releases the iPad using iOS
       As of Nov. 2011 40 million sold.
       Samsung releases the Galaxy tablet using  Google's Android OS
2011 - At the Consumer Electronics Show in January, over 80 new tablets were announced.
       By 3Q Android had made headway into the tablet market, but still only had 25%
2011 - HP discontinues webOS hardware.
       It will continue support of webOS software it acquired from  Palm in 2010.  

Articles:
"Soft machines: A philosophy of user-computer interface design" SIGCHI (1983), by Nakatani & Rohrlich at Bell Laboratories
Key Apple Multi-Touch Patent Tech Approved, 2009

Links:
Mini and Personal Computing Timeline
Multi-touch - Wikipedia
Mobile Computing
It's a photo finish: Android, BlackBerry and iOS are tied in US smartphone share (2010)
Android leads US market share, iOS may have stopped growing, RIM is still falling -- Engadget Dec., 2011