Originally posted by: mchammer
What would be the smallest possible size a phone could be made right now, just a basic phone, no camera or fancy screen.
The limiting factors would tend to be the size of the battery, keypad, antenna, etc. The actual electronics that make up the transceiver and 'phone' (if you don't need embedded Java, a web browser, fancy graphics, Bluetooth, etc.) are pretty damn small.
Look at, e.g. the Motorola RAZR; without the fancy screen you could probably just cut the top half off. If you didn't need a keypad (use voice dialing with some logic to let it recognize spoken numbers, and/or upload a phone book from a PC), you might be able to shrink it a bit more, but the battery, antenna, and mic/speaker will still limit you. You could ditch the mic/speaker, I guess, and only have it work with a headset.
That would probably give you something about 2"x3"x.3". That's around the size of a few credit cards stacked on top of each other (and is pushing the limits of how small you can reasonably make something like a phone). As was said, without a significant breakthrough in batteries (or other portable energy sources, like micro fuel cells), you can't really make any portable device requiring significant power a lot smaller.