Nickname
A nickname is given to a Denjuu or Dino for personalization, or to help differentiate it from others of its kind.
Telefang 1
When befriending a Denjuu in Telefang 1, the T-Fanger has the option to nickname a Denjuu. It is entered using the D-Shot. Nicknames are restricted to six characters (kana or numbers). While nearly all unevolved Denjuu have no more than 6 kana, there are a few Denjuu that can be found in the wild and are more than 6 kana long. The most notable is Firekokko (ファイアーコッコ), where its default nickname will shorten to ファイアーコ. Denjuu's nicknames do not change at all upon evolution, even if they were not nicknamed.
Denjuu that are found in events, like the starter Denjuu Crypto and Fungus, among others, cannot be nicknamed. There is an exception to this however, any Denjuu received via link connection (either traded or won in VS) can be nicknamed upon receipt.
Bootlegs
In the bootlegs Pokémon Diamond and Jade, nicknaming is impossible, either because of a glitch or because the bootleggers could not make the phone type out Latin characters. As a result, Denjuu are auto-nicknamed to the first six characters of their bootleg name, with the exception of the Lampgera received in Iris, which has the glitchy nickname "o". Also, due to numerous bootleg Denjuu names being longer than their original Japanese names, the 6-character limit is far more prominent (for example, Crypto, known as Kuribute in the bootleg, will be called "Kuribu".)
Telefang 2
Nicknaming in Telefang 2 is similar to Telefang 1, but the 6-character limit was removed and is now 8 characters (the maximum possible length for a Denjuu name). Also, it is possible to input Latin characters (albeit only in capital letters) instead of just kana or numbers. Denjuu received in trades cannot be given new nicknames.
Dino Device 1
The nicknaming system in Dino Device 1 is more robust than that of either Telefang game. A Dino can be nicknamed after being received through the Gachasta, or captured wild. Nicknames have an 8-character limit, and can be comprised of hiragana, katakana, upper- and lower-case Latin characters, numbers and mathematical symbols, punctuation, and a selection of 50 kanji. Nicknames cannot be changed after being given.