Data switching (on iPhone: Allow Cellular Data Switching) is a dual SIM setting. When it's on, your phone can use mobile data from your second line too, not only from the line you picked for data. Apple says the iPhone then uses data from both plans "depending on coverage and availability". When it's off, only your chosen data line uses mobile data.
So should you allow cellular data switching when traveling? If you travel with a travel eSIM next to your home SIM, the safe answer is usually no. Turn it off, make the travel eSIM your data line and turn off data roaming on your home line. This guide explains what the setting does on iPhone and Android, what "Primary" and "Secondary" mean, and which settings to use abroad.
What is cellular data switching?
A dual SIM phone can hold two lines, for example your home SIM and an eSIM. Both lines can make calls and send texts. But only one line at a time is your mobile data line (Apple: Using Dual SIM with an eSIM).
Cellular data switching (also called mobile data switching or automatic data switching) lets your phone use the other line for data as well. Apple describes two effects on iPhone:
- Data from both plans: your iPhone can use cellular data from either line, depending on coverage and availability.
- Data during calls: when you're on a call on the line that isn't your data line, that line takes over data for the length of the call. Without the setting, mobile data doesn't work during that call.
It also helps you receive calls on your other line while you're on a call (more on this below). New to dual SIM? Read what a dual SIM is first.
Is data switching the same as data roaming?
No. Data roaming lets a line use mobile data on a network outside its home country. Data switching decides which of your two lines can use data. The two are linked, though: if your home line has data roaming on and data switching can pick it, your phone may use your home carrier's roaming data. Apple's iPhone User Guide warns that you may incur roaming charges if Data Roaming is on and you're outside your carrier's network area (Apple: Use Dual SIM on iPhone). See should you keep data roaming on or off.
Allow Cellular Data Switching on iPhone
This setting only matters when you have two lines turned on.
Where to find it
- Open the Settings app.
- Tap Cellular, then Cellular Data.
- Tap the line you want to use for data.
- Turn Allow Cellular Data Switching on or off.
In the UK and some other countries, the menus say Mobile Service or Mobile Data, and the setting is called Allow Mobile Data Switching. It's the same thing.
What "Primary", "Secondary" and "Travel" mean
These are only labels. Your iPhone gives each line a name so you can tell them apart in Phone, Messages and Contacts. You can change a label in Settings > Cellular: tap the line, then Cellular Plan Label, and pick a label or type your own (Apple). Naming the lines "Home" and "Travel" makes the next steps easier.
A label doesn't decide which line uses data. When you set up a second line, your iPhone asks which line is your default for calls and texts, and which one to use for cellular data. You can also use one line for cellular data only. You can change the data line at any time in Settings > Cellular > Cellular Data.
Why it matters for calls on your other line
Say your travel eSIM is your data line and you're on a call on your home line. Apple says that to receive calls on your other line during a call, you need Allow Cellular Data Switching on, and Wi-Fi Calling on for that line. Otherwise the incoming call goes to voicemail. Apple also notes that this in-call data switching won't work while you're using Data Roaming. Abroad, that's most of the time.
Data switching on Android: Pixel and Samsung
Android phones have a similar option with a different name.
- Google Pixel: Settings > Network & internet > SIMs > Automatic data switching. Google says you need it, along with mobile data on both SIMs and Wi-Fi calling on the second SIM, to use both SIMs for calls at the same time (Google: Use dual SIMs on Pixel).
- Samsung Galaxy: Settings > Connections > SIM manager > Data switching. It switches mobile data between your two SIMs to keep the best coverage (AT&T: Galaxy S25 data switching).
Menu names can differ a little by model and software version. On both, you also choose which SIM is your default for mobile data in the same menu.
Should I allow cellular data switching when traveling?
Usually not, if you use a travel eSIM and keep your home SIM on. Your home carrier may charge for roaming data. If data switching can use your home line, a weak signal on the travel eSIM could send some data through your home line. And the main extra it gives you on a call, data during the call, doesn't work while you're roaming anyway.
The safe setup with a travel eSIM and your home SIM
- Install the travel eSIM on Wi-Fi before you fly and label it "Travel".
- Choose the travel eSIM as your data line. On iPhone: Settings > Cellular > Cellular Data, then tap the travel eSIM (Apple: Use eSIM while traveling internationally). On Pixel or Samsung, pick it as your mobile data SIM.
- Turn off Allow Cellular Data Switching (Automatic data switching on Pixel, Data switching on Samsung).
- Turn off data roaming on your home line. On iPhone: Settings > Cellular, tap your home line, then Cellular Data Options, and turn off Data Roaming (Apple: About cellular data roaming). On Pixel: Settings > Network & internet > SIMs, tap your home SIM and turn off Roaming.
- Turn on data roaming for the travel eSIM when you arrive, so it can connect to local networks.
- Keep your home line on for calls and texts if you want to stay reachable. Calls and texts on it can still cost roaming fees, so check your carrier's rates. Wi-Fi calling can help.
With iOS 26 and later, your iPhone may show a Turn On Travel eSIM prompt when you arrive. If you pick Travel eSIM and Current eSIM, the travel eSIM is used for data. Apple warns that you might still incur roaming fees from your home eSIM, so the steps above still apply. More detail in our guide to the correct roaming settings for an eSIM.
When turning it on makes sense
- You're at home with two domestic lines, like work and personal, and want data and incoming calls on both during a call.
- Your home plan includes roaming in the country you visit at no extra cost, and you're happy for it to be a backup.
A data-only eSIM for your travel line
The setup above works best with a travel eSIM that handles all your data, while your home SIM keeps your number. A data-only plan does just that. Pick the region you're visiting:
Europe, United States and Asia · data only, your home number stays on your phone · Find your destination
Pros and cons of cellular data switching
Pros
- You can keep using mobile data during a call on your non-data line.
- You can receive calls on your other line while you're on a call (with Wi-Fi calling on).
- Your phone can fall back on the other line's data if one line has no coverage.
Cons
- It doesn't pick the cheaper line. It works on coverage and availability, not on price.
- Abroad, it can use your home line's roaming data if data roaming is on for that line.
- You have less control over which line uses your data.
To keep an eye on which line used what, check your usage per line. On iPhone, here's how to check your data usage.
How to turn off cellular data switching
- iPhone: Settings > Cellular > Cellular Data, then turn off Allow Cellular Data Switching.
- Google Pixel: Settings > Network & internet > SIMs, then turn off Automatic data switching.
- Samsung Galaxy: Settings > Connections > SIM manager, then turn off Data switching.
Don't see the option? You need two active lines. Set up your second line first: here's how to set up and manage a dual eSIM.
FAQs
What does data switching mean?
It means your dual SIM phone can use mobile data from both of its lines, not only from the line you chose for data. On iPhone the setting is Allow Cellular Data Switching. On Pixel it's Automatic data switching, and on Samsung it's Data switching.
Should I allow cellular data switching with an eSIM?
When you travel with a travel eSIM and your home SIM, it's safer to turn it off. Make the travel eSIM your data line and turn off data roaming on your home line. At home, with two local lines, turning it on is fine.
Is cellular data switching the same as roaming?
No. Roaming means using a network outside your carrier's country. Data switching means using data from your second line. If both are on for your home line abroad, you may pay roaming charges.
What is the difference between Primary and Cellular Data on iPhone?
"Primary" is a label for one of your lines. "Cellular Data" is the setting that says which line uses mobile data. Your Primary line can be your data line, or you can pick your other line for data.
What is data switching in SIM manager?
On Samsung Galaxy phones, Data switching in SIM manager lets the phone switch mobile data between your two SIMs to keep a connection. Turn it off abroad if your home SIM would charge you for roaming.
Will I miss calls on my home number with it turned off?
Not when you're free. Your home line still rings. While you're already on a call on your other line, an incoming call on your home number can go to voicemail. Wi-Fi calling helps here.
Can I make calls with a data-only travel eSIM?
Not normal phone calls on a new number, but you can call with apps like WhatsApp or FaceTime over its data. Here's how to make phone calls with a data-only eSIM.
