How is it that by just putting a SIM card into your phone you have access to 4G/5G?
In: Technology
The “SIM” in “SIM card” stands for “Subscriber Identity Module”. It is basically a way of storing an “IMSI” or “international mobile subscriber identity” number and encryption key that uniquely identifies the device, associating it with a user that has been authorized to access the cellular network. There are cell towers all around that the phone can talk to, but only if the user has paid for access (or it is an emergency call).
Just having a SIM card isn’t sufficient, you need that SIM card to be associated with an active account to be provided the service. Once your cell phone can communicate with the cell towers it can pass information in the form of phone calls or it can communicate data for things like web pages.
The SIM card contains a key used to authenticate you on the wireless network. So it’s similar to knowing a wifi password. The wifi was always there, but you only have access to it once you put in the password. The SIM card has a hardcoded password which it automatically uses to connect to the cell network. This password is connected to an account on the network carrier, so it will only work if the associated account is active.
A SIM card in and of itself does not connect you to the internet; rather, it tells the mobile networks around it that you are authorized to connect to the internet (because you’ve bought phone minutes, or are paying a subscription, or however else you pay for your phone). It’s like a video game keycard.
Your phone always has the capacity to use mobile internet, but when you attempt to connect to the network, the network checks your SIM card to make sure you’re allowed to connect, and decides whether or not you have access based on that.
The phone always has the ability to connect to the cell system.
In fact, in the United States, its actually legally mandated that emergency calls (911 and, sometimes, local police and fire numbers) always connect even if the phone has no valid plan. Obviously, this law does not mandate there be actual coverage for your location, but, if the phone can connect to a tower, the tower *must* accept the connection and connect you to the emergency system.
What the SIM card does is give the phone an unique subscriber number (fyi, SIM stands for “Subscriber Identity Module”) that the cell system uses to identify the phone so the network can link your phone to your plan. With this, the cell network knows whether you are part of their network or not, and if not, how to bill your provider for your usage. The network can also use this data to throttle your usage or otherwise limit your access based on your plan.
A SIM card acts as your phone’s ID and password to your mobile carrier. It’s like going to a cool club. To get in you gotta show your ID and give the secret code.
You show your ID and password and the mobile phone carrier lets you on to their network, which has connection to the internet
A SIM card isn’t a mechanism that is needed to get the phone connected to the Internet. It’s the mechanism that providers use to make sure you have paid (or will pay) for the connection to the Internet.
Lots of answers, not many explained like a 5 year old so here it goes.
Your phone can do all of these things by itself. But it can’t do it without connecting to a network. It’s like a tree house. You can see it’s there, you know your friends are doing some awesome shit up there, but they won’t let you in without a password.
The SIM card is the password.
A phone is fully functional and connects to the cellular network automatically. Before they let you USE that network, they need to know who you are, and that you’ve paid for your ticket to ride.
That SIM is your ticket to ride the cellular network. Otherwise, you’re only allowed to make emergency calls.
Your phone can still be used for games and apps, as long as you have an account with Google/Apple/Samsung/etc. You just need to use WiFi for Internet access. You can even use WiFi for WiFi phone calls/video calls. Once you are away from that WiFi hotspot, you’re screwed. That’s when the cellular network connection takes over, and you need that “ticket” again.
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