Nokia beat Apple to it... maybe?
There have been lots of allegations that Apple's iPad and iPhone do not deserve the credit to the invention -- Especially if your name is Frank Nuovo and you have worked for Nokia, you would agree, but would have to admit that you have missed the chance of a lifetime.
Nuovo, formerly vice president and chief designer at Nokia, told the Wall Street Journal that Nokia had developed an iPhone-like device in 2002. There was not much information about this product, other than it had a touchscreen and allowed its user to browse the web, find restaurants and play games. Nuovo also said that Nokia had a tablet that was finished in the late 1990s. He told the Journal that he was not happy when he heard that Apple would be releasing a tablet and he is similarly unhappy when people tell him that the iPhone is unique.
Unfortunately, there is not much detail in the article and we have no idea what Nokia had in mind with its prototypes, other than the company decided to hold them back from a commercial release. In Apple's defense, the iPhone and iPad are, of course, more than just hardware and some may claim it is the combination of software and hardware that has made them so successful. Did Nokia have the software to go along with its hardware? We may never know.
However, we should also note that Nokia was not the only company that had a tablet in the late 90s and early 2000s. Back then, we called them webpads and they were released from virtually any company that remotely had hardware experience. You could find products from Honeywell to 3Com - all of which were ahead of their time and suffered from lack of wireless connectivity, short battery running times and unimpressive displays. So, Nuovo can have hard feelings about the iPhone, but an entire computer industry should blame itself for having missed the right time to come out first with a decent tablet.