A SIM card is a small, plastic electronic chip with a unique serial number that is inserted into certain types of wireless phones, tablets, hotspots, etc. to enable service with a cellular network. They come in three different sizes - Standard, Micro, and Nano.We activate your plan and associate a SIM card with it. The network then allows the device using that SIM card to send and receive data.A hotspot works like a wireless, mobile router. They connect to the cellular network like a phone, but they do not make phone calls or send text messages. They broadcast a Wi-Fi signal in their vicinity and allow you to to connect any Wi-Fi device to them. Once connected, those devices can utilize the unlimited high-speed data of your plan.For example, if you activate a hotspot that supports 10 devices, you could simultaneously connect any combination of up to 10 smartphones, game consoles, smart TVs, security cameras, etc. and each can take advantage of the unlimited data.