Dual SIM means your phone can hold two mobile numbers at the same time and use both. On most modern phones that is the physical SIM you already have, plus an eSIM you add in software. Both numbers stay live: calls, texts and verification codes arrive on whichever number they were sent to, and you decide which line is used when you start something yourself.
That is the whole trick behind a spare UK number. Nothing about your everyday number changes — no new handset, no swapping SIMs in and out, no forwarding.
What dual SIM actually means
A SIM is what tells the mobile network who you are. An eSIM does the same job, but it is a profile downloaded onto a chip already inside the phone rather than a piece of plastic you slot in. If your phone supports eSIM, it can usually run that eSIM alongside its physical SIM — two numbers, two separate lines, one device.
- Your existing SIM keeps your existing number, plan and contacts. It is untouched.
- The eSIM adds a second UK mobile number (07…) on a real network — a proper mobile line, not an app-based number.
- Both lines can be registered to the network at once, so both can receive calls and texts.
- You pick which line is the default for calls, texts and mobile data.
If you are not sure your handset can do this, start with does my phone support eSIM. The two things that matter are that it is eSIM-capable and that it is unlocked.
Which line does what
Once two lines are active, your phone asks you to assign a few jobs. This is the part people worry about, and it takes about a minute.
| Job | Set it to | Why |
|---|---|---|
| Calls and texts you make | Your main number | Family and friends see the number they already know. |
| Mobile data | Your main number | Your existing allowance keeps working exactly as it does now. |
| Incoming calls and texts | Both lines, always on | Anything sent to either number reaches you without switching. |
| Chat app sign-up and codes | The spare number | A separate account is tied to the spare line, not your personal one. |
Setting it up
- 1
Add the eSIM
Scan the QR code we send you, or tap the install link on the phone itself. The profile downloads over Wi-Fi in a couple of minutes. Full walkthrough in how to set up your eSIM.
- 2
Name both lines
When the phone asks, label the new line something like "Spare" and leave your existing one as "Personal". You can rename them later.
- 3
Keep your main number as default
Choose your existing line for outgoing calls, texts and mobile data. This is the single most important choice — get it right and your day to day does not change at all.
- 4
Check both lines are live
Send a text to the new number from another phone, and make a normal call from your usual number. Two ticks and you are done.
- 5
Use the spare number where you want it
Sign up for a separate chat account with it, or hand it out instead of your personal number. See see the WhatsApp plan for the version most people start with.
Per-contact line preferences
Phones remember which line you last used with a given contact, and most let you pin a line to a contact permanently. That is genuinely useful once you have a spare number in play.
- Pin clients, customers or marketplace buyers to the spare line so replies never go out from your personal number.
- Leave family, friends and your GP on your main line.
- Before you send, glance at the line label shown in the compose bar. It is always visible.
If your reason for a second number is keeping the personal one out of circulation, keep your number private covers the habits that make it stick.
What does not change
Your number, your contract, your contacts, your messages, your apps. Adding an eSIM does not touch any of them, and removing it later does not either. If you decide the spare line is not for you, deleting the profile puts the phone back exactly where it was.
eSIM Chat is a spare UK mobile number delivered as an eSIM, powered by eSIM Copilot and part of Mindszi.
Common questions
Will my normal number still work exactly as before?
Yes. Your existing SIM and number are untouched. As long as you keep it set as the default for calls, texts and data, your day to day is identical.
Can both numbers receive calls and texts at the same time?
On a phone that supports two active lines, yes — anything sent to either number reaches you. If your handset only allows one active line at a time, you have to switch between them, which is much less convenient.
Do I need two phone plans?
You need one plan per number. Your existing plan stays with your existing number, and the spare eSIM line has its own. Nothing is shared between them.
Which line uses my mobile data?
Whichever one you choose. Most people set data to their main line so their existing allowance carries on as normal, and use the spare line mainly for calls, texts and codes.
Get a spare number
A real UK line that lives on your phone as an eSIM, beside the SIM you already have. Installed in minutes.