This is specific to Sense UI phones!Note: The picture shows some options specific to HTC's Sense UI

We have already discussed the functions of the four main buttons featured on most Android phones. One vital button was omitted: the on/off button. This button is more commonly used to boot up your phone, or cause the screen to goto sleep to save battery power if clicked once. Holding this button causes a menu to appear, with different options depending on what phone you have.

Most phones will have silent mode, airplane mode, and power off options. Phones with HTC's Sense UI (Droid Incredible, Evo 4G, Desire, etc) will have a couple extra: toggle vibrate mode and toggle mobile network. The former turns on vibrate and turns off sound for all notifications (email, phone calles, etc) while the latter will toggle your 3G or 4G data connection. This is really useful if you want to save battery when using a WiFi network.