eSIM, dual SIM and roaming: Mobile networks in everyday life

In short: An eSIM is a built-in SIM activated with a code; dual SIM allows two plans in one phone, and roaming governs use abroad.

In more detail: The SIM identifies you in the mobile network (number, plan). Besides the classic plastic card there is now the eSIM, a chip in the device onto which the provider loads a profile.

In Depth

eSIM

Instead of swapping a card you scan a QR code or use the provider’s app, and the plan is active. Advantages: quick provider change, several profiles storable, nothing to lose or bend, good for wearables. Disadvantages: moving to a new device requires transfer or re-activation by the provider, with a defect or empty battery no simple swapping. Not all devices and plans support it.

Dual SIM

Two numbers or plans in one device (SIM + SIM, SIM + eSIM or eSIM + eSIM). Practical for private and business, or a cheap data plan next to the main number. You decide which number is used for calls, messages and mobile data. Check battery consumption and the costs of both contracts.

Roaming

In the EU/EEA “roam like at home” applies: you use the plan (minutes, SMS, data) as at home, usually with a fair-use limit for data. Outside the EU (Switzerland, UK, Turkey, USA …) charges can be high: check the plan before travelling, book a travel pack, buy a local or travel eSIM or use Wi-Fi. Switch off data roaming when you do not need it and enable cost warnings.

Security

SIM swapping: criminals have your number transferred to their SIM to read SMS codes. Protect your account with the provider with a PIN/password, use authenticator apps instead of SMS for two-factor, and enable the SIM PIN. If you suddenly lose the network for no reason, ask the provider immediately.

See also: Mobile contracts and plans, 5G mobile network, Two-factor authentication, NFC