Updated to add iPhone 5, and Retina iPad support

iOS Simulator Device.scpt

set selectedDevices to choose from list {"iPhone", "iPhone (Retina 3.5-inch)", "iPhone (Retina 4-inch)", "iPad", "iPad (Retina)"} with prompt "Choose device type:" default items {"iPhone"} without multiple selections allowed
if selectedDevices is not false then
	set selectedDevice to item 1 of selectedDevices as string
	set thePListFolderPath to path to preferences folder from user domain as string
	set thePListPath to thePListFolderPath & "com.apple.iphonesimulator.plist"
	
	tell application "System Events"
		tell property list file thePListPath
			tell contents
				set value of property list item "SimulateDevice" to selectedDevice
			end tell
		end tell
	end tell
end if