United Kingdom
United States
Spain
Morocco
Turkey
Tunisia
Thailand
The biggest eSIM mistakes have nothing to do with the eSIM. They happen in your phone's settings, usually because both SIMs are fighting over which one handles your data. Get the settings right before you fly and your travel eSIM handles all your data at local prices while your UK number keeps working for calls and texts. Get them wrong and your UK SIM can quietly rack up roaming charges while the eSIM you paid for sits idle.
This is the exact checklist we give our own customers. It takes five minutes at home on WiFi. If you have not bought a plan yet, start at the SimplySim destinations page.
The Goal: Who Does What
A phone with two SIMs needs to know which line does which job. For travel, the correct split is:
- Travel eSIM: all mobile data
- UK SIM: calls and texts only, with its data roaming switched off
Every setting below exists to enforce that split.
iPhone: Step by Step
After installing your eSIM (Settings, then Mobile Service, then Add eSIM, then scan the QR code we email you), work through these:
- Label your lines. Settings, Mobile Service, tap each line and rename them to something obvious like UK Number and Travel Data. Future you will thank present you.
- Set mobile data to the travel eSIM. Settings, Mobile Service, Mobile Data, choose your travel eSIM.
- Turn OFF Allow Mobile Data Switching. This toggle lives on the same screen. Left on, your iPhone can silently fall back to your UK SIM for data, which is exactly the roaming bill you are trying to avoid.
- Set default voice line to your UK number. Settings, Mobile Service, Default Voice Line. Calls and iMessage stay on your own number.
- Turn ON Data Roaming for the travel eSIM only. Tap the travel eSIM line, enable Data Roaming. Travel eSIMs technically operate as roaming SIMs, so this must be on for the eSIM. Then tap your UK line and make sure its Data Roaming is OFF.
Android: Step by Step
Menu names vary slightly between Samsung, Pixel and others, but the logic is identical:
- Install the eSIM. Settings, Connections (or Network and Internet), SIM Manager (or SIMs), Add eSIM, scan the QR code.
- Set the travel eSIM as your data SIM. In SIM Manager, under Preferred SIMs, set Mobile Data to the travel eSIM.
- Keep calls and texts on your UK SIM. Same screen, set Calls and Messages preferences to your UK line.
- Enable data roaming on the travel eSIM only. Open the travel eSIM's own settings and switch Data Roaming on. Check the UK SIM's settings and switch its roaming off.
The Three Mistakes That Cause Almost Every Support Ticket
- Data roaming off on the eSIM. The plan looks dead on arrival. It is not; the phone is just refusing to connect. Roaming ON for the travel eSIM is required.
- Mobile data still pointed at the UK SIM. Everything works, which is the problem. You come home to a roaming bill because the eSIM never carried the data.
- Deleting the eSIM to fix a problem. Never delete an active eSIM while troubleshooting. Deleting removes the profile from your phone. Restart the phone or toggle aeroplane mode instead.
What About WiFi Calling?
If your UK network supports WiFi calling, leave it enabled. On hotel WiFi your normal calls and texts then work with no roaming involved at all, which pairs nicely with the eSIM handling data everywhere else.
Test It Before You Board
- The eSIM shows in your SIM list with your chosen label
- Mobile data is assigned to the travel eSIM
- Data roaming: ON for the eSIM, OFF for your UK SIM
- Default calls line is your UK number
The eSIM will show no service until you reach your destination. That is normal. It activates when it first connects to a network in the country of your plan.
Final Thoughts
Five minutes of settings at home saves both the roaming bill and the airport stress. Install, label, point data at the eSIM, lock roaming to the right line, and you land connected. Check your phone supports eSIM on the device compatibility checker, then pick a plan on the SimplySim Deals Page.
