Since users touch the screen with their fingertips, touch targets (hit areas) for UI components need to be large enough for users to initiate actions without frustration. If you use BlackBerry UI components, you don’t need to worry about the size of the touch target for each UI component. The sizes are designed to be large enough for users to touch with a finger. The design also allows users to be a bit "sloppy" when touching the screen. This means that the touch area is forgiving and allows users to be less precise but still carry out the action that they want.
If you create custom UI components, be aware that the size of the touch target depends on the pixels per inch (PPI) for the screen. If you are designing your application for different BlackBerry devices, create touch targets to accommodate the pixel densities for each screen size.
Best practices for custom UI components