Steve is looking for a motion activated security camera that can run on a cellular network. Leo says that all security cameras are motion activated these days. DropCam and Nest would be the natural choice, but they rely on Wi-Fi.
Leo recommends the Eagle Eye Nubo. It has 2G, 3G and LTE. It's also weather resistant. But he'll want to be sure that it is supported by his carrier. He'll have to get the SIM from them anyway.