From Bulbapedia, the community-driven Pokémon encyclopedia.
A P★DA, Pokémon Digital Assistant, is an electronic device owned by Wes in Pokémon Colosseum and by Michael in Pokémon XD: Gale of Darkness, in lieu of a Pokédex. The P★DA keeps track of a Trainer's ID No., their money, as well as their playing time. It also has other features, detailed below.
While only certain Trainers can receive a Pokédex from a Pokémon Professor, it appears that just about anyone can own a P★DA, at least in Orre.
Pokémon Colosseum's P★DA, closed
Pokémon Colosseum's P★DA, opened
In Pokémon Colosseum, the P★DA can also be used to send and receive e-mail and keep track of the Trainer's PokéCoupons. It also has a ringtone that can be customized to the preferences of the user. Additionally, Wes's P★DA was upgraded with the Snag List, a list of the Shadow Pokémon created by Cipher.
Another feature of the P★DA is the Strategy Memo, which is awarded to Wes by a teacher inside of the Pre Gym. It contains a list of all Pokémon encountered, giving the user their type, Ability, height, weight, and appearance. The only drawbacks are the inability to use it in battle, and the fact that one must update regularly with the teacher who awarded Wes with the device.
Pokémon Colosseum's P★DA, opened and showing information
Pokémon XD's P★DA, closed
In Pokémon XD, the P★DA has a new interface, along with a new feature. As in Colosseum, the device keeps track of PokéCoupons, has a Strategy Memo and e-mail, and can be upgraded to keep track of Shadow Pokémon. Its new feature is a Poké Spot Monitor, which alerts the player whenever there is activity by wild Pokémon at one of the three Poké Spots.
Unlike the P★DA in Colosseum, this version has the Strategy Memo installed at the start, and updates it automatically.
Poké Spot Monitor
The Poké Spot Monitor is an addition to the P★DA in Pokémon XD: Gale of Darkness. It is given to Michael by Duking at the Rock Poké Spot after a TV broadcast. It allows Michael to monitor how many Poké Snacks are left at a Poké Spot, and see if any Pokémon can be found at one. It is fitted with an alarm which triggers when there is activity at any Poké Spot. Most of the time it is a Wild Pokémon that is found at one of the Poké Spots, but sometimes it is a mischievous Munchlax that belongs to a fellow Orre citizen.
Pokémon XD's P★DA, opened and showing the information