Like the previous games, when you connect to other players over Wireless or WiFi, you don't appear as the in-game trainer but rather as a specific trainer class. In the previous games, these were changed by a character in-game and the trainer classes available were based upon your ID Number.
Black & White however, abolishes both the method of change and the restrictions of the trainer classes. Here, you can change your online avatar through your Trainer Card. Under your character's name will be the trainer class and you can cycle through them just by tapping the class on the screen.