Windows Phone 7 actually requires 6 hardware buttons, not 5
It’s widely believed that Windows Phone 7 requires 5 hardware buttons, but it looks like, in fact, there are 6 of them.
Apart from Start, Back, Search/Bing, camera button and power button, there is also a volume (up and down) button that’s listed by Microsoft as being required.
The up and down volume buttons are used to adjust either the overall device volume (music, video, apps, ringtones), or the in-call conversation volume. Also, “when a user receives a phone call, touching any of the volume buttons will silence the ringtone.”
As mentioned lots of times until now, the first Windows Phone7 devices will be available in time for this year’s holidays. For the beginning, five manufacturers will release WP7 devices: HTC, Samsung, LG, Dell and Assus.