From Eclipse
To disable the Internet connection, go to Eclipse and do
menu Window -> Show view -> Other -> Android -> Devices
Now select your running emulator and again go to:
menu Window -> Show View -> Other -> Android -> Emulator Control
Now in that… set Data to Unregister from Home.
From Device and Emulator
On the device or in the emulator, go to:
Setting -> Wireless & networks -> Airplane Mode -> OK