How a multi network SIM works
A single network SIM belongs to one operator and can only use that operator’s masts. A multi network SIM is issued by a provider that has agreements with several operators. When the router powers up, the SIM can register on any of the permitted networks. If that network is lost, the SIM can register on another one.
Because the fixed IP address is assigned by our provider’s core network rather than by the radio network, the address stays the same whichever network the SIM happens to be using. Your firewall rules, port forwards and VPN configuration do not change.
Network selection: steered or strongest signal
Multi network SIMs choose networks in one of two ways, and it is worth knowing which you are buying.
- Steered. The SIM prefers one network and only moves when that network is unavailable. This keeps behaviour predictable and can keep costs down.
- Router led. The router scans the networks and chooses the best signal or the best performance, for example with the operator selection features on Teltonika and ProRoute routers.
Failover is not instant. When a network drops, the router has to notice, detach and register on the next network, which usually takes from a few seconds to a couple of minutes. For sites that cannot tolerate that gap, pair a multi network SIM with a second SIM in a dual SIM or dual modem router.
Why the VodafoneThree merger matters for multi network SIMs
Until recently, a SIM that could use EE, O2, Vodafone and Three gave you four independent networks. After the merger, Vodafone and Three completed their network integration in 2026, and a Vodafone or Three SIM can now connect through either company’s masts across most of the country. That improves coverage for both brands, but it also means Vodafone and Three are no longer fully independent of each other.
In practice a multi network SIM now gives you three network groups: EE, O2 and VodafoneThree. That is still far more resilient than a single network SIM. If you are designing for maximum resilience, make sure your primary and backup connections sit on different groups. Read our full guide to the merger.
Multi network, multi-IMSI or roaming?
| Multi network | Multi-IMSI | Roaming | |
|---|---|---|---|
| How it gets several networks | One identity with access to several UK networks | Several identities on one SIM, each with its own home network | A home network plus roaming agreements worldwide |
| Main strength | Simple UK resilience | Local identity in each country, fewer roaming limits | Coverage across borders |
| Typical use | UK sites, CCTV, telemetry, backup broadband | Long life IoT, international device estates | Vehicles, plant, touring equipment |
See multi-IMSI SIM cards and roaming fixed IP SIM cards for more detail.
Multi network SIMs with a dynamic IP
If you do not need to reach the router from outside, you can still benefit from multi network failover with a dynamic IP SIM. These are ideal for backup broadband, card payment terminals that connect outbound to their processor, and devices that report to a cloud platform. They cannot be used for inbound remote access, because they sit behind carrier-grade NAT.
Questions we are often asked
Does my fixed IP change when the SIM switches network?
No. The address is assigned by the provider core network, so it stays the same on EE, O2, Vodafone or Three.
How quickly does a multi network SIM fail over?
Typically from a few seconds to a couple of minutes, depending on the router settings and how the first network fails. A dual SIM router with SIMs on different network groups can recover faster.
Is Three included?
Three can be included. Since the VodafoneThree network integration, Vodafone and Three share masts in most areas, so adding Three mainly helps in places where the shared network is not yet in use.
Can I choose which network the SIM prefers?
Yes. Tell us your preferred network and we can steer the SIM to it, or you can use your router to select networks manually.
Will a multi network SIM work in my existing router?
Almost certainly. Any 4G or 5G router that accepts a standard SIM and lets you set the APN will work. Some router features, such as automatic operator scanning, make the most of multi network SIMs.