# Dual SIM

> A phone feature that lets two SIM lines work at once, physical or eSIM, so your home number stays reachable while a travel eSIM handles data.

Source: https://viasimo.com/glossary/dual-sim/
Also known as: dual-SIM, dual SIM dual standby, DSDS

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Dual SIM is a phone feature that lets two SIM lines work in the same device at once: two physical SIMs, a physical SIM plus an eSIM, or two eSIMs, depending on the model. Both lines can receive calls and texts, while one of them is chosen to carry mobile data at any given moment.

For travellers this is the feature that makes [eSIM](/glossary/esim/) travel plans so convenient. Your home SIM stays in the phone, reachable for calls, texts and the one-time codes banks insist on sending, while a travel eSIM supplies affordable local data. Nothing gets swapped, lost or left in a drawer at home.

## The classic travel setup

The standard configuration takes about a minute. Set the travel eSIM as your mobile data line; keep the home SIM active for voice and SMS; then turn [data roaming](/glossary/data-roaming/) on for the eSIM and off for the home SIM so it cannot generate surprise charges. Our [dual SIM travel setup guide](/magazine/dual-sim-travel-setup-guide/) covers this step by step, including labelling the two lines so you always know which is which.

Two confusions are worth clearing up. First, most phones are dual standby rather than dual active: both lines are registered to their networks, but if you are on a call on one line, the other may be briefly unreachable on some models. Second, apps tied to your phone number do not move when your data line changes; WhatsApp keeps working on your home number over the eSIM's data connection, which is exactly the trick explained in [keeping your WhatsApp number abroad](/magazine/keep-whatsapp-number-abroad-esim/).

A concrete example: sitting in a Paris cafe, your phone shows two rows of signal bars. A call from home rings through on your usual number, while maps and photo uploads run through the travel eSIM. The caller has no idea you are abroad, and your home carrier has nothing to bill. Check [device compatibility](/device-compatibility/) to confirm your model supports dual SIM with eSIM, since a few budget and regional variants do not.