Fixed IP SIM Cards have been used for many years with 3G and 4G routers and more recently new 5G Fixed IP SIM Cards have been made available for use with 5G routers. The reason that you needed a Fixed IP SIM Card in your router, rather than using a standard 4G SIM Card directly from EE, Vodafone, O2 or 3 Mobile was becuase in order to remotely connect to your 4G router, you would need to know the IP address. Using a standard 4G SIM Card would mean that whilst your router would have an IP address, this would be a private IP address, belonging to your mobile network provider. This private IP address would be issued using CGNAT (Carrier grade NAT) and would sit behind a public IP address owned by your mobile network. This meant that if you connected a PC to your 4G router and connected to the internet with a PC and opened a web browser and visited www.showmyip.co.uk then the public IP address will be shown, and this would be the one owned by your standard network provider. However your router would be on a different, private IP address and would typically be one of hundreds of devices, all with private IP addresses, issues by the mobile network, sitting behind this single public IP address. This would mean that you would not be able to directly connect to your router, nor would port forwarding work to connect to the devices on the LAN side of your router be possible because in order for port forwarding to work you first of all need to access the router. You would need to ask your network provider eg. EE, to remove all the devices connected behind the single public IP address and ask them to forward all the traffic to that IP address ONLY to your router and also ask them to ONLY provide this public IP address to your router, every time the router re-connected to their network. Of course they will not do this for you – why should they?
But this is exactly what a Fixed IP SIM Card network provider does for you. They allocate your SIM card with a single, public IP address so when your 4G router connects to the mobile network using the specific APN (Access Point Name) provided to your for use with your Fixed IP SIM. This way you can have your 4G Internet connection with a dedicated IP address just for your SIM and router connection. This will enable you to remotely connect to your router and therefore be able to use the port forwarding feature of your router to connect to the devices on the LAN. This is the same for 3G, 4G and 5G SIM Cards. So if you need to remotely connect to your 3G Router, 4G Router or 5G Router then you will need to use the appropriate 3G, 4G or 5G Fixed IP SIM.
You can get Fixed IP SIM’s with either a public IP address or private IP address. In the case of using a SIM card with a public IP address, this will allow you to connect directly to your router from any device connected to the Internet. This also means that your router and devices on the LAN are accessible by anybody with an Internet connection so you should ensure that your router security settings are correctly configured to prevent unauthorised access to your router admin pages as well as any devices that can be connected to using port forwarding, these should also have all their security features fully configured.
The alternative to using a Public IP Fixed IP SIM, is to use a Private IP Fixed IP SIM which will still have a fixed IP address and use a specific APN to allow it to connect directly to your Fixed IP SIM provider, but it will be a private IP address that cannot be directly communicated with from the Internet. In this case you will need to first of all create a VPN from your PC to your Fixed IP SIM network provider and once your PC is connected to their VPN service you can then connect to your routers and connected devices, making this method much more secure.
Of course, all these 4G and 5G SIM cards were issued by different Fixed IP providers so if you have a 4G Router using a Fixed IP SIM and you wanted to change to a different provider you would need to visit site and swap the physical SIM card over with the new SIM issued by your new provider. This seems okay for one or two installations, but imagine if you had hundreds of 4G routers installed and wanted to switch to save money on your monthly rentals then you would have to visit hundreds of sites just to switch the SIM card, making it prohibitive. This is where a true eSIM router solution comes in and a Fixed IP eSIM service provider who can activate their Fixed IP eSIM service on your eSIM router to enable remote connection. When it comes time to switch eSIM network service provider your new provider can simply apply the settings remotely to your eSIM router saving time and money when switching eSIM provider.