These are IP addressable cameras. They are always on, just like your router. They can be viewed and controlled remotely by any internet connected computer, iPad, or iPhone (smartphone). If you are viewing them from an iPad or iPhone, you will need to purchase a very inexpensive app. I recommend Foscam Pro, uFoscam, or IP Cam Viewer. All three are very good.
Wireless camera setup requires a basic understanding of the wireless portion of your network. Specifically, you need to provide the camera with your network name, password, and encryption type. You need to do the initial setup with the camera connected to the router with an ethernet cable because the camera has no way of knowing what those settings are right out of the box. Once you've completed the wireless configuration, you can unplug the ethernet cable.
Viewing and controlling the camera remotely with an iPad or iPhone is more involved. You need to understand DDNS (Dynamic Domain Name Server) technology and port forwarding so that this information can be provided to the camera. The router also requires some additional configuration. It's not as scary as it sounds. I can walk you through all of it if you decide to get the camera.
Generally, there is no advantage to the hardwire connection. Wireless is much more convenient. You can put the camera wherever you wish as long as there is a 120 VAC receptacle nearby. The camera does not run on batteries.
As to your question about a SIM card, these cameras do not use SIM cards. If you wish to store video, then you must purchase a third party video security program such as Blue Iris ($50) for PCs or Evocam ($30) for Macs. These programs must be running on a computer that is always on to have full benefit of the software. They also offer tremendous capability and flexibility over the built in software of the camera. I highly recommend either one.