Select your travel eSIM for cellular data, configure roaming separately for each line, and decide whether to keep your home line active for calls and SMS. If you want data use to stay on your chosen travel line, leave automatic data switching off. A default voice line is a separate choice; it does not determine which plan supplies internet access.
Planning an iPhone 18 Pro upgrade? Start with our country-specific iPhone eSIM guide. This settings guide assumes your exact model supports the required line combination. Menu wording can vary by region and iOS version.
Checked September 12, 2026. Cover photo: iPhone 18 Pro and Pro Max, courtesy of Apple Newsroom.
Four controls that answer different questions
| Control | What it decides | Travel starting point |
|---|---|---|
| Cellular Data | Which line supplies mobile internet | Select the travel plan |
| Data Roaming, inside each line | Whether that line may use data outside its carrier's own network | Home: off; travel: follow plan instructions |
| Allow Cellular Data Switching | Whether iPhone may change the data line | Off for a fixed data-line choice |
| Default Voice Line | Which number is the default for calls | Choose an active line with voice service, if needed |
Apple documents separate data and voice selections. The table is a starting configuration for someone buying separate travel data, not a statement that every home roaming plan is unsuitable.
Set up the roles before departure
- Identify both plans. In Settings, open Cellular or Mobile Data. Give the lines clear labels, such as Home and Japan Trip. Avoid leaving two similar carrier names that you could confuse at arrivals.
- Choose the data line. Open Cellular Data and select the travel eSIM when your plan's activation instructions say to use it. Review the switching control before leaving this screen.
- Review roaming individually. Open Home and locate Data Roaming, sometimes under Cellular Data Options. Turn it off if you do not intend to use home-carrier roaming data. Then inspect the travel line separately; enable roaming there when its instructions require it.
- Check the calling number. Choose your intended voice line if keeping voice service. Before an important call or message, inspect the number displayed in the app instead of assuming the data choice changed it.
- Save your plan instructions. Keep the order reference, activation conditions and support contact accessible. Use the Trips eSIM installation guide for installation; do not delete an installed profile to change these preferences.
Apple's roaming instructions explain the per-line controls. Trips eSIM's installation instructions require checking each product's activation policy; installing and starting validity are not always the same event.
Should automatic data switching be on?
For a traveler who wants one chosen plan to supply data, off is the clearer starting point. This is an editorial recommendation based on the control's purpose, not a guarantee about your carrier bill.
There is a tradeoff: Apple says cellular data will not work during a voice call on the other line when switching is disabled. Enabling switching can let the calling line handle data during that call, but Apple says this behavior does not work while Data Roaming is in use. Availability and additional charges depend on the carrier. See Apple's Dual SIM explanation.
If a map stops updating during a home-number call, finish the call or use available Wi-Fi before reviewing your settings.
Home-number SMS needs its own decision
A travel data connection does not move your home phone number or its SMS service to the travel plan. If a bank sends a one-time code by SMS, keep the home line enabled and confirm that its carrier can deliver messages at your destination. Turning that line off means you should not rely on it for incoming carrier SMS.
Apple distinguishes internet messaging from SMS and advises checking that the required phone line is on. Wi-Fi Calling can support SMS where available, but it needs carrier support; a working internet connection alone is not proof that your bank's code will arrive. See Apple's messaging guidance.
Keeping both lines active may still produce home-carrier roaming fees. Ask about incoming calls, outgoing texts and any travel-pass triggers before departure. Apple also flags this possibility in its international eSIM guidance.
Example: a new phone and a seven-day Japan trip
Imagine Maya has upgraded her iPhone for a week in Japan. She wants maps on travel data, but an airline account sends codes to her existing number.
Her preparation has three parts: confirm the airline offers an alternative sign-in method, ask her home carrier about message delivery and charges in Japan, and select a plan that covers the whole visit. At arrival, she checks the line labels against her saved order before testing a small webpage with Wi-Fi off.
If the webpage loads but a code does not arrive, she has learned something useful: internet access and home-number message delivery need separate checks. She uses the airline's alternative method rather than repeatedly changing every network setting.
Frequently asked questions
Does choosing a travel eSIM change my phone number?
Choosing a data line does not port your number. Check the calling or messaging identity separately when you need to contact someone from a particular number.
Can I turn roaming on for the travel line only?
Yes. Inspect each line's settings separately and use the travel plan's instructions. A single screenshot of one line does not verify the other.
Does disabling home data roaming block every possible charge?
No. It is a data control, not a spending cap for voice, messaging or carrier services. Confirm your home plan's terms.
Where should I start if the settings look correct but data fails?
Check coverage, validity and the supplied network instructions. Contact Trips eSIM support with the order reference and non-sensitive error details; keep activation codes private.
Compare Trips eSIM destinations after checking device compatibility, coverage, validity and the services your itinerary needs.