FIRST!! (I think): Windows 98 Tablet
Here is a Paleo-Tablet concept from around '98. I was pretty optimistic that by '01, IBM could make a Thinkpad fit into just the LCD section and the whole thing not weigh 7 pounds. The idea was to have this adapter thing that would accept your Qualcomm Thinphone(BTW, it still has the best ergos ever in a candybar IMHO). The blazing IS-95 14.4kbps wireless dialup connection available at the time would allow you to surf, umm, decently. Remember most sites back then were still designed for dialup.