Dual SIM is one of the best technological innovations for travellers. The idea is simple: your home physical SIM stays active for calls and texts while the eSIM provides cheap, local internet. So you enjoy the advantages of both worlds.
How does dual SIM work?
Modern smartphones can handle two SIM cards at once:
- Physical SIM (slot 1): Your home carrier's SIM card
- eSIM (digital): The travel data plan (eSIM Surfer)
The phone handles both at once, but for different tasks:
| Function | Which SIM? | Why? |
|---|---|---|
| Internet data | eSIM | Cheap, local prices |
| Receiving calls | Physical SIM | Your home number stays active |
| Making calls | Physical SIM (or VoIP) | Your usual number |
| Receiving SMS | Physical SIM | Bank confirmations, codes |
| WhatsApp, Viber | eSIM data | Free, uses the eSIM's data |
Setup on iPhone
1. Install the eSIM (see our eSIM activation guide)
2. Set the SIMs' roles:
- Settings → Mobile Network → Mobile Data → select the eSIM
- Settings → Mobile Network → Default Voice Line → select the physical SIM
3. Set data roaming:
- eSIM profile → Data Roaming: ON
- Physical SIM profile → Data Roaming: OFF (this is the most important step!)
Setup on Android (Samsung / Pixel)
1. Install the eSIM
2. SIM manager settings:
- Settings → Connections → SIM manager
- Mobile data: eSIM
- Calls: Physical SIM
- SMS: Physical SIM
3. Data roaming:
- eSIM → Data roaming: On
- Physical SIM → Data roaming: Off
The most important rule: data roaming off!
This is the most critical setting, which many people forget:
ALWAYS turn off data roaming on the physical SIM!
If you leave it on, the phone may route data through your home carrier's expensive roaming — especially if the eSIM temporarily loses signal. This can result in a large bill in a single day.
Cost savings with dual SIM
Example: 1-week holiday in Turkey
| Item | Without roaming (dual SIM + eSIM) | Full roaming |
|---|---|---|
| Internet (10 GB) | €8.99 (eSIM) | Expensive |
| Receiving calls | Roaming fee (or Wi-Fi calling) | Same |
| WhatsApp calls | Free (on eSIM data) | Free (but on expensive data) |
| Total | €8.99 | Expensive |
Tips for perfect dual SIM use
- Wi-Fi calling (VoWiFi): If your carrier supports it, you can receive calls over hotel Wi-Fi with no roaming fee
- SMS codes: Bank confirmation texts arrive on the physical SIM — this doesn't need data roaming, but network registration is required (the phone connects to the local network in roaming mode)
- WhatsApp priority: Ask your contacts to call you on WhatsApp rather than by phone — WhatsApp calls are free on the eSIM's data
- iMessage: iPhone's iMessage service also runs on the eSIM's data, so it's free
Summary
Dual SIM is the smartest travel solution: eSIM for internet (cheap, local prices), physical SIM for your home number (calls, texts, bank codes). The most important thing to do: turn off data roaming on the physical SIM. This gives you a 70–85% saving compared with full roaming.