Yes, it's actually a phone, stuck in the back cover of your average leather-bound Filofax. Trust a Japanese manufacturer to come up with a way to make the most old-school object all techy and stuff.
The Willcom NS - or WS026T - is a Toshiba make, powered by Windows CE 5.0 with a 4.1-inch WVGA screen and Wi-Fi support. It has just 235 MB of internal memory, but has a microSD slot expandable by up to 16GB. Instead of widgets, its applications are cutely named ‘jiglets' - you can customise your screen with RSS feeds, maps and notes jiglets. You can also remove it from its Filofax cradle for straight up PDA use.
According to Akihabara News, the NS uses Willcom's proprietary WSIM technology and (of course) only works in Japan, on the PHS network.