The pokedex is a small handheld device, designed as an "encyclopedia" of pokemon. It contains exactly 150 pokemon, and is designed in the shape of a rectangle, and slides in and out, like a modern flip-phone.
It is first given to you with only the basic 150 pokemon, and it only has the ability to show a pokemon's area, cry, size, and weight. It's second update, the Pokedex V.1.2, it now shows it's size in comparison to you, the trainer, and it shows the different male and female forms of the pokemon. It's final upgrade, the Pokedex V.1.3, can show an extra 50 pokemon that are now able to catch throughout the two other regions.