There are three hardware buttons required on all Windows Phone 7 Series chassis’s.
Figure 1: Hardware buttons.
Start: Powers on the device. If the phone is on, then pressing this button takes you to the start page. Programmers do not have access to the Startup Button event in the phone API.
Back: Press this button to return to previous screen. Programmers have access to the Back button event, allowing apps to provide custom navigation scenarios within each application.
Search: By default this launches search on phone OS. Programmers have access to the Search button event.
