Buttons on the panel won't work.
Menu - nothing
Home - nothing
Back - leave aplications
I have android 2.1
For my (Dutch) blog, I made a poll, asking people which button layout people prefer for Android phones.
Please vote bij clicking on one of the links :)
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Poll: Welke Layout?
HTC One just features 2 buttons i.e HOME and BACK no MENU key. Obviously menu key is not required by many apps on holo interface it is somewhat useful in certain apps.
Htc one will utilize the home key long press for menu. Initially it will be frustrating but once getting used to it wont make you feel awkward
Multitasking comes by DOUBLE TAPPING the home key.