The F-04B isn't your average touchscreen QWERTY slider. If you want to slim things down, the 3.4-inch screen and slide-out keyboard can be separated, and you can also attach an 854 x 480 pico-projector in place of the keyboard.
When separated, the keyboard communicates with the screen via Bluetooth, and can act as a keyboard (duh), microphone, speaker, and game pad. It also serves as a remote control when the pico-projector is used.
Apparently the F-04B's 12.2-megapixel camera takes "nice pictures for a phone", but the touchscreen could do with being a little more responsive.
The phone was first shown as a prototype at CEATEC 2008, but Akihabara News says that Fujitsu and Japanese carrier, DoCoMo, have "officially" announced it as the Separate Keitai F-04B. No word yet on what OS it runs, availability, or pricing (inside or out of Japan). Definitely a unique idea. [Akihabara News]