The short answer
Dual SIM means your phone can hold two mobile lines and keep both switched on at the same time. On most current phones that means one physical SIM card plus one eSIM, or two eSIMs. You choose which line is the default for calls, which for texts and which for mobile data.
For travel, the classic set-up is simple: your own SIM stays on for calls and texts on your normal number, and a travel eSIM handles mobile data. You stay reachable, SMS codes still arrive, and data comes from a prepaid plan instead of your home operator's roaming.
There are a few limits to understand, mainly that only one line can use mobile data at a time and that a call on one line can affect the other. The rest of this guide explains these in plain terms.
The kinds of dual SIM
Phones combine SIMs in different ways. You do not need to know the technical names, but they help when reading phone specifications.
- Physical SIM plus eSIM: the most common arrangement on recent iPhones, Samsung Galaxy and Google Pixel phones.
- Two eSIMs: many newer phones can run two eSIM lines at once, with no physical card at all. Some phones, such as recent iPhone models sold in certain countries, have no physical SIM tray and rely entirely on eSIM.
- Two physical SIMs: common on some Android phones, particularly in markets where dual-SIM handsets are popular. These phones may or may not also support eSIM.
Stored versus active
Most eSIM phones can store several eSIM profiles, but only a limited number can be active at the same time, typically two lines in total. You can keep a travel eSIM installed between trips and switch it on when you need it, without deleting anything.
What 'dual standby' means in practice
Most phones work in a mode often called dual SIM dual standby. Both lines are registered on their networks and can receive calls and texts, but the phone has one set of radio hardware that it shares between them. That leads to two practical rules.
Only one line uses mobile data at a time
You pick a single line for mobile data. When the travel eSIM is selected, all your apps use it, and your own SIM does not use data at all. You cannot split apps between lines in the usual settings.
A call on one line can affect the other
While you are on a traditional phone call on one line, the other line may not be able to receive calls, and incoming calls may go to voicemail. Some phones offer an option that lets your own line use the data line's connection to stay reachable during calls; on iPhone this setting is called 'Allow Cellular Data Switching'. Whether it helps, and whether your home operator supports it, varies.
The recommended set-up for travelling
This set-up works for most travellers using a data-only travel eSIM such as Spidot.
- Default voice line: your own SIM. People can call you on your normal number.
- Messages (SMS) line: your own SIM, so bank and verification codes arrive as usual.
- Mobile data line: the travel eSIM.
- Data roaming on your own SIM: off. This prevents your home operator charging for data abroad.
- Data roaming on the travel eSIM: on, once you arrive. A travel eSIM connects through partner networks, which your phone treats as roaming.
- Data switching between lines: off, unless you have a specific reason to turn it on. This keeps data strictly on the travel eSIM.
On iPhone
Open Settings, then Mobile Data or Cellular. You will see both lines listed. Set your default voice line, choose the travel eSIM under Mobile Data, and open each line to set its own Data Roaming switch. Our install guide for iPhone walks through adding the eSIM itself.
On Android
Menu names vary between makers. On Samsung Galaxy phones look in Settings, Connections, SIM manager. On Google Pixel look in Settings, Network and internet, SIMs. Set the preferred SIM for calls, messages and mobile data, then open each SIM to set its roaming option. See our guides for Samsung and Pixel.
Label your lines clearly
When you add a second line, your phone lets you give each one a name. Use obvious labels such as 'Home' and 'Travel'. It sounds trivial, but when you are tired at an arrival hall and looking at two lines both called 'Secondary', a clear name saves a lot of guesswork.
Labels also help in the dialler and in messages. On many phones you can choose which line to call from before you dial, and the label shows which one you are using.
Calls and texts in a dual-SIM set-up
With a data-only travel eSIM, every traditional call and SMS uses your own SIM, and your home operator charges at its usual roaming rates. Calls made in apps such as WhatsApp, FaceTime or Signal run over data and therefore over the travel eSIM.
If you need a number that works for normal calls in the destination, a Data + calls plan or a local SIM can provide one. On a dual-SIM phone you could then choose per call which line to use. For most trips, though, app calls over data are enough, and our guide to keeping your WhatsApp number explains how messaging apps behave.
Other good uses for dual SIM
Travel is the most common reason to use two lines, but not the only one.
- Work and personal numbers on one phone, with separate defaults and do-not-disturb rules.
- A backup data line in areas where one network is weak and another stronger.
- Frequent trips to the same region with a no-expiry eSIM that stays installed and is switched on when needed.
- Keeping a home number after moving abroad, while using a local SIM day to day.
Does my phone support dual SIM with eSIM?
Dial *#06#. If an EID number appears, the phone has an eSIM chip, which means it can almost certainly run an eSIM alongside a physical SIM or a second eSIM. You can also check your phone against our list.
The phone must also be carrier-unlocked. A phone locked to your home operator may refuse a second operator's eSIM, or accept the profile but not connect. If you bought the phone on a contract, ask your operator whether it is unlocked before you travel.
Between trips: switching lines off rather than deleting
When you get home, you do not need to delete the travel eSIM. Switch the line off in your SIM settings and choose your own SIM for mobile data again. The profile stays stored on the phone and takes up no tray space.
Keeping it is worth it if you have a no-expiry balance or expect to add more data for a future trip to the same destination. If you are sure you will never use it again, you can delete it, but remember that a deleted eSIM usually cannot be reinstalled from the same QR code. When in doubt, switch it off and decide later.
One small habit helps: after a trip, check that your own SIM is selected for mobile data and that its data roaming is still off, so nothing surprises you on your next journey.
Common dual-SIM problems and fixes
- Data is not working on the travel line: check that it is selected for mobile data and that data roaming is on for that line. See installed but no data.
- My home SIM used data abroad: data switching between lines may be enabled, or the home SIM was selected for data. Turn off data switching and data roaming on the home line.
- I miss calls while on another call: this is a limit of dual standby. Ask important contacts to message first, or use app calls.
- iMessage or FaceTime shows the wrong number: in Settings, Messages and FaceTime, check that your own number is selected.
- Battery drains faster: two active lines use slightly more power, especially where signal is weak. Turn off the line you are not using if battery matters more than reachability.
- Wider problems abroad: our guide on what to do if your eSIM is not working abroad works through the full checklist.
Frequently asked questions
Can I use both SIMs for data at the same time?
Will having two SIMs cost more?
Can I switch which SIM is used for data during my trip?
Do I need to remove my physical SIM to install an eSIM?
Can I turn off one line without deleting it?
Plans for this trip
Check the plans and live prices before you go. You receive the QR code by email right after payment.