just a note - balance is more a question of the distribution of weight rather than size/volume. As can be seen from the image, the upper/tablet section is largely empty, and this is likely why the lower part, even if thinner, has roughly the same weight as the upper one. So, unless the lower part's center of gravity is close to the hinge, it can be quite stable.

mer - apparently the guys who make this welcome all OS-es, it's really close to the beagleboard, so mer is plausible

3g - with the internal slots, this not really a question, you can stick in any usb 3g dongle with linux support. same for additional bt/wifi/gps stuff. these internal slots are in a sense a poor man's cardbus slot