If the phone freezes you can force turn it off. Holding down the power button and the volume up button for 5 seconds will cause it to kill all process and turn off the power. However I don't recommend doing this unless you cannot get the phone to respond for a long period of time. I usually have to do this if my system uptime is too high because usually I will have run too many processes and the screen will just freeze in the middle of a game or web browsing. The down side to this is you might wind up causing an app to no longer work right. I had to do it last night and now I am having trouble getting my live wallpaper to work.
Holding Power and Volume up till it vibrates three times in succession is the equivelant to pulling the battery for these phones (since they don't have a removable battery)
