What is a multi SIM?

Three meanings of multi SIM

The rest of this page takes each in turn. If you came here because a network or reseller offered a "multi SIM deal", it is almost certainly the first meaning.

1. Multibuy: several SIMs on one account

The most common business meaning is simply buying several SIM only plans together on one account. Networks package this as multibuy or multi-line plans for teams. Three Business, for example, has Multibuy SIM plans for up to 9 unlimited data SIMs (UK only; fair use applies in Go Roam destinations), with optional inclusive roaming, as physical SIMs or eSIMs, managed online or through the Three app.

Which plans qualify, how many SIMs an account can hold and what changes as you add lines are set by each network, and we confirm them for your team at quote. Multibuy suits small teams, and larger organisations usually move onto plans built for many lines, with shared or individual data and an account portal; our pages on fleet SIM cards and SIM only for small businesses cover both ends. When you compare multibuy plans, look at the price per SIM over the whole term, including annual price rises, rather than the first month. Our guide on how to compare business SIM only deals walks through it.

2. Multi-network SIMs

A multi-network SIM can attach to more than one mobile network. If one network has no signal where the device is, it can use another. The idea is resilience: the device stays connected even where any single network's coverage is weak.

In the UK, multi-network SIMs are used mainly for IoT and M2M devices: vehicle trackers, payment terminals, alarm signalling, remote sensors and cameras. These devices often sit in fixed places that nobody chose for their signal, or travel across the country, so being able to use more than one network is valuable. Our page on IoT SIM cards explains how these SIMs differ from phone SIMs.

For staff phones, a multi-network SIM is less common. Phone users are usually better served by a network with good coverage where they actually work, which each network's coverage checker will show, and our guide to business SIM only networks explains how to approach that. If a supplier offers a multi-network SIM for phones, ask exactly how it switches networks, which services (calls, texts, data) work on each, and what happens to your number.

Tell us about the devices and where they sit, and we can help you work out whether a multi-network option suits them.

3. One number on several devices

The third meaning is having one phone number work on more than one device. There are two common forms.

A second device that shares your number

A cellular smartwatch or eSIM-enabled tablet can be set up to share the number and allowances of your phone, so calls and messages reach you even when the phone is elsewhere. Vodafone Business, for example, describes its OneNumber Connectivity Plan as a way to share your airtime and data allowances across a smartwatch or eSIM-enabled tablet, without Wi-Fi or the phone nearby. These arrangements are specific to each network and each device, so check compatibility first.

One phone, two numbers

This is the reverse: one phone with two numbers on it, usually a physical SIM plus an eSIM. It is how staff can carry a business number and a personal number on the same handset. Three Business says a dual SIM device can run two numbers on one phone, with two eSIMs or an eSIM and a physical SIM. EE Business also describes eSIM as a way to keep business and personal numbers on one device. Our page on eSIM SIM only plans explains the set-up, and business SIM vs personal SIM covers why keeping work and personal lines separate matters.

Which kind of multi SIM does a business need?

• Several staff need SIM only plans: multibuy or a multi-line business plan on one account; start with business SIM only plans
• Devices must stay connected in poor coverage: a multi-network IoT SIM may help; see IoT SIM cards
• Staff want work and personal numbers on one phone: a business eSIM alongside their personal SIM; see eSIM SIM only
• Someone wants their number on a watch or tablet: a network's number-sharing plan, if their devices support it
• Tablets and laptops need data: not a multi SIM at all, but a business data only SIM for each device

If you are not sure which applies, describe what you are trying to achieve rather than the product name; it is usually clear quickly.

How we help

We supply business SIM only plans on EE Business and Three Business, and we can also supply O2 Business and Vodafone Business, including several SIMs on one account and eSIMs for dual-number phones. We can help you:

• Work out which kind of multi SIM you actually need
• Work out the cost per SIM over the whole term, not just the headline monthly price
• Move existing numbers across with PAC codes when you switch
• Set caps and record which SIM belongs to whom from the start

What we can supply is confirmed at quote. Contact us with the number of people and devices you need to connect, and we can suggest which kind of multi SIM fits.