You don't need to remove the sim card. What will happen is you won't be able to use EDGE and you'll only be able to update things through Wi-Fi. If you try and make a call, it will use any of the available networks it can find, but you can also go into the settings, and tell it to use a carrier of your choice, or change it from automatic, to manual. I am currently in Ireland and have been using the Wi-Fi whenever I find a hotspot. Works fine. Everything works but the phone functions obviously. But like the previous poster said, you can make calls, but it will be super expensive and probably not worth it unless it's an emergency.