Dual SIM travel: keep your home number, get cheap local data
The setup that actually works: home line for SMS 2FA, travel eSIM for data, switching as needed.
If your phone supports two SIMs (and almost everyone's does now), this is the setup we run:
- SIM 1: home line — data off, roaming off, but the line itself enabled. It still receives SMS for 2FA. Costs you nothing while abroad if you never use data.
- SIM 2: travel eSIM — data on, set as the default data line.
Outgoing calls and SMS default to whichever you set as the "default voice line". Most people leave home for calls (so your friends see your normal number when you call them back) and set travel for data.
On iPhone
Settings → Cellular, set:
- Default Voice Line → home
- Cellular Data → travel eSIM
- Allow Cellular Data Switching → off (otherwise iOS will roam your home line on the cheapest carrier deal it can find — surprise charges)
On Android
Settings → SIM cards, set:
- Mobile data → travel
- Calls → home (or "Ask before calling" if you want to pick per-call)
- SMS → home
What about iMessage and WhatsApp
Both keep working with your home number even when home data is off. They route over the travel eSIM's data. So friends still text you at the same address; they just appear in the chat instead of as SMS.
The 9eSIM trick
Even if your phone only has one embedded eSIM slot, the physical SIM tray gives you a second slot. Put a 9eSIM card in there, load 50 destination profiles onto it, and you've got a programmable second line. Now you can dual-SIM in every country instead of being stuck with whatever travel eSIM you happened to install at the airport.
What to turn off the second you land
- Visual voicemail on the home line (some carriers charge for retrieval even via WiFi)
- Background app refresh for big apps on the home line specifically — they sneak data over roaming if both lines are on
- iCloud Backup on cellular