A traditional router always used to be a box that physically plugged into "the internet" (a WAN, or wide area network) on one side, and your own LAN (local area network) on the other side. Exactly what those wires plugged into, varied.
Then someone invented DSL and cable broadband
. So there were two more specific kinds of routers, the DSL router, which plugs into your phone
line instead of a conventional WAN port, and that can only plug
into a DSL line on the WAN side.
And the "cablemodem", which can only plug
into a cable provider's network on the WAN side.
Either one of these may be a "modem" which connects only one computer to the WAN, or a full-blown router that connects multiple computers
(a true LAN) to the WAN. On most of the home routers, you can connect 4 home computers
on physical LAN sockets, versus only one on the cheapest units.
That's ignoring the issue of whether a router supports WiFi
, which usually can handle 16 more connections or better.
So, now there is an alternative to DSL or cable broadband
, and that's cellular broadband. Cellular companies have been, well, squirrelly about data connections. They invent, rent, sell, all sorts of options and adapters and then turn around and say "that's impossible, we'll never do it" usually the year before they make something standard. (sigh)
Somewhere along the way, some genius decided to make routers that use a SIM card and connect to the cellular companies' broadband directly, instead of a conventional WAN. In theory...your cell phone
acting as a mobile hot spot (which no one allowed just a few years ago, duh) or a dedicated mobile hot spot box, could so the same job. In practice, a SIM card router is more powerful, should support faster connections, and should also generally be faster and more secure because it has a better dedicated processor supervising the connections AND enabling security
options that your hot-spot-phone wouldn't have.
Really very logical. No magic, but then again, it seems like everyone forgot to advertise that these things exist. (Duh.)
Note that you often cannot use the same SIM card in a "computer" or "tablet" that you use in a "phone". Some companies may let you stick the card in anything and use the same amounts of data, etc. Other companies automatically check the device ID (the IMEI number) and their networks will automatically change your billing, or disable the device, if it has been swapped out. You have to ask the cellular company, and take what they say on faith.