I am not sure, but I believe you can. Mine has a sim card slot, but I do not have a sim card and I am getting the free 3G service through Verizon without the card. When I got the Chromebook, I had to call Samsung and they walked me through setting it up for the service.
I do not think so. My other dissapointment is that (i) touch screen does NOT work; (ii) key board cannot be operated in dim light/dark as key pad does not light up - I thought all those came with my purchase.