A newly published BlackBerry Patent application entitled Ergonomic Navigation Cursor Controller For a Handheld Mobile Communication Device specifies technology for a "navigation button" dedicated to controlling the movements of a cursor on a BlackBerry screen.
The Abstract is rather specific. It calls for:
An ergonomic cursor navigation controller for a handheld mobile communication device generally includes a navigation button having a ringed and waved upper surface and may further include an execution button disposed within a perimeter defined by the ringed and waved upper surface. The navigation button is provided for navigating a cursor about an electronic graphical display of the handheld mobile communication device. The ringed and waved configuration of the controller facilitates improved tactile operation of the controller and reduces the occurrence of pressing incorrect buttons on the handheld mobile communication device.
In this Patent app's art, Figure 22 offers an informative view of what's being proposed here. The controller is element 34 in the grab: