Den Den Mushi

These are the odd "phone snails" that are used throughout the series. They come in a variety of colors and shapes and have multiple functions. The snails act as a number of devices including: rotary phones, fax machines, and cellular wrist watch devices. It's unknown how the Den Den Mushi are able to communicate with one another over such great distances. When they are used, the snails speak in sync with the caller's voice, as well as sometimes imitating the facial expressions of the caller. Fans have speculated that the snails may be naturally telepathic, and somehow this ability has been harnassed in lieu of wireless phone technology in the One Piece world. When not in use, the Den Den Mushi are usually inert, either sleeping or in a dazed state. Other types of Den Den Mushi include:

Kuro Den Den Mushi
A (Black) Den Den Mushi, is used by the Navy to intercept calls between pirates or other miscreants.

Baby Den Den Mushi
The Baby Den Den mushi is fairly small and portable, but incapable of international calls.

Golden Den Den Mushi
This Den Den Mushi is a special kind that is used to summon the Buster Call.

Silver Den Den Mushi
The Silver Den Den Mushi is like an alarm used to receive the Golden one's Buster Call request.