From Wikifang, a definitive guide to Telefang, Dino Device and BugsiteDenjuu World. They are found in a variety of shapes, sizes, and types. The Denjuu World is also populated by Antenna Trees, which give out peculiar electronic waves which Denjuu are attuned to. All Denjuu are born from a particular Antenna Tree called the Life Tree. The first humans to make contact with the Denjuu World were Sanaeba Corporation, a pharmaceutical company.
 D-Shot and Telefang
Denjuu are fully capable of talking with humans, and after their discovery they were given advanced mobile phones called D-Shots in order to aid in communication. Denjuu also like to participate in competitive battles, and the D-Shots allow them to call their friends to help. Battling in this way is referred to as Telefang. A human who befriends Denjuu and participates in Telefang with them is known as a T-Fanger. If a Denjuu is defeated in Telefang, it may be impressed enough with its opponent's strength to offer its phone number to them.
The player can call a Denjuu friend outside of battle to get it to be their current partner. This Denjuu will follow behind the player everywhere, and automatically enter first in all battles. When using an item, it is used on the current partner automatically in Telefang 1. In Telefang 2, one can choose which Denjuu to use the item on. The player can only have one partner Denjuu at a time, though they can be swapped outside of battle.
When a player enters a battle, the current Denjuu partner will automatically enter the battle, together with either 0, 1, or 2 other Denjuu friends of the player's, using his/her D-Shot to call them. How far away they live from the current position of the player determines the number of turns before the Denjuu reach the player and join the battle. Depending on each Denjuu's personality, they may also get lost along the way and might turn up late, or not reach at all.