The menu-button was removed from devices which run Android 3.0 and higher and is now considered "deprecated". There is a nice Blog-post about why, how to use the new ActionBar and how to keep legacy support for older applications:
If your app runs on a device without a dedicated Menu button, the
system decides whether to add the action overflow to the navigation
bar based on which API levels you declare to support in the <uses-sdk>
manifest element. The logic boils down to:
- If you set either
minSdkVersion
or targetSdkVersion
to 11 or higher, the system will not add the legacy overflow button.
- Otherwise, the system will add the legacy overflow button when running on Android 3.0 or higher.
- The only exception is that if you set
minSdkVersion
to 10 or lower, set targetSdkVersion
to 11, 12, or 13, and you do not use ActionBar,
the system will add the legacy overflow button when running your app
on a handset with Android 4.0 or higher.
If you're starting Android development or you're creating a new application now, don't use this kind of menu but rather use the ActionBar.
Helpers are available in the "Support Library" for backwards-compatibility:
The ActionBar is not supported by the library. However, when creating
your Options Menu, you can declare which items should be added to the
Action Bar when it's available (on Android 3.0 or later).