By default your PhoneGap application will contain system menu button, even on those systems (Android 4.0+) that doesn’t support this button any more (i.e. applications written for this system should not use this button; it is handled anyway and you can use it, if you really wish to).
On most new devices user pressing this button will be simply ignored by system and nothing will happen. So, this problem reduces itself to purely aesthetic means (whether you care about seeing that unusable button on system bar, when your app is active, or not).
However, there are reports, that PhoneGap applications crashes on small group of devices, when user presses this not handled system menu button. In this case, more radical solutions must be considered.
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