专用的发送、结束和后退按钮，以及小巧的滚动导航键，让G 1比iPhone更加灵活，但操作也更加复杂。

The dedicated Send, end and Back buttons, and the tiny trackball for scrolling, make the G1 more flexible than the iPhone, but also more complicated.

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许多设备提供不同类型的用户输入机制，例如键盘，滚动球，或五方向的导航键。

Many devices provide a different type of user input mechanism, such as a hardware keyboard, a trackball, or a five-way navigation pad.

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