From the menu, select View | Toolbars | Device. This will give you a toolbat
with 1 active button. Press it to launch an emulator (you'll have to choose
between the available emulators and a real device).
You can get the Smartphone emulator from
http://www.microsoft.com/downloads/details.aspx?familyid=a6c4f799-ec5c-427c-807c
-4c0f96765a81&displaylang=en.
Other companies have emulators available too, so you should check the
developer sections of their websites.