Calls, texts and OTPs with a data eSIM: how it actually works
Last checked: August 2026
A data eSIM is one of the simplest ways to get online abroad, but there is one thing worth understanding before you travel, because it causes most of the confusion: a data eSIM gives you internet, not a phone identity. It does not come with a phone number, and it cannot make normal calls or send text messages. What it does, it does very well: fast, affordable mobile data the moment you land.
Here is exactly how the pieces fit together, so nothing surprises you on your trip.
The short version: voice and texts stay on your home SIM over its roaming, and data comes from your Slashtel eSIM. Keep both SIMs in the phone, and turn off data roaming on the home SIM so you only pay for the cheap eSIM data.
You have two lines, and they do different jobs
Modern phones support dual SIM, which means your Slashtel eSIM works alongside your existing SIM rather than replacing it. Think of it as two lines living in one phone:
- Your home SIM carries your phone number. It handles standard calls, SMS text messages, and any one-time passcodes your bank sends by text.
- Your Slashtel eSIM carries your data. It handles the internet: maps, browsing, email, WhatsApp, video calls and hotspot.
You keep both in the phone. You just tell the phone to use the eSIM for data.
What runs on your Slashtel data
Anything that uses the internet works on your eSIM, with no phone number needed:
- WhatsApp messages, voice notes and WhatsApp calls
- Video calls on FaceTime, Google Meet, Zoom, Microsoft Teams
- Maps and navigation, ride-hailing, email, browsing, social media
- Hotspot and tethering to a laptop or tablet
For most travellers this is everything they actually use, which is why a data-only eSIM is enough on its own for the trip.
What still needs your home SIM
Three things do not run on the eSIM, because they belong to your phone number:
- Your phone number itself, so anyone calling or texting your usual number
- SMS text messages, including bank and login one-time passcodes (OTPs)
- Standard cellular calls, which route through your home carrier and are charged at its roaming rates
The important one is OTPs. Banks, UPI apps and many logins send a code by SMS to your number. That code arrives on your home SIM, so keep it in the phone.
The setup, in three steps
- Install the Slashtel eSIM before you fly, on Wi-Fi at home. Scan the QR code from your email. It sits dormant until you arrive.
- Set the eSIM as your default data line in your phone's mobile-data settings once you land.
- On your operator SIM, switch roaming on for calls and texts, but switch data roaming off. Roaming on is what lets calls, texts and bank OTPs reach your number abroad; data roaming off means you never pay for roaming data. All your internet runs on the eSIM instead.
That is the whole thing. Number and OTPs on the home SIM, data on the eSIM, no roaming bill.
If you are keeping an overseas number active
If you are travelling from India, the UK or elsewhere and need to keep a home number alive for bank OTPs or UPI, make sure that prepaid number has enough balance and validity to stay active for your whole trip. If it is an Indian number running low, you can top it up from abroad with a card on the recharge page before you leave.
The bottom line
A Slashtel eSIM is data only. It gives you the internet, not a number. Keep your home SIM in the phone for your number, calls and OTPs, run everything else over the eSIM data, and you get the best of both: cheap data abroad and your usual number still reachable, with no roaming surprises.
Questions, answered
Can I make phone calls with a Slashtel eSIM?
Not standard cellular calls. A Slashtel eSIM is data only, so it has no phone number and cannot place or receive normal calls or SMS. You can make calls over the internet using WhatsApp, FaceTime, Google Meet, Zoom and similar apps, which run on your eSIM data. If you need a normal cellular call, that goes through your home SIM at your home carrier's roaming rates.
Will I still receive my bank OTP while abroad?
Yes, as long as your home SIM stays in the phone and is reachable on a network. Bank one-time passcodes are sent by SMS to your phone number, and your number lives on your home SIM, not on the Slashtel eSIM. Keep the home SIM in the second slot with data roaming switched off, and OTPs keep arriving. If your home number is prepaid, make sure it has enough balance and validity to stay active.
Do I keep my phone number?
Yes. Your number stays on your home SIM, which you keep in the phone. The Slashtel eSIM does not give you a new number and does not replace your existing one. It simply adds a data line alongside your home SIM.
How do I avoid roaming charges on my home SIM?
Keep the home SIM in the phone for calls and SMS, but turn off data roaming for it in your phone settings, and set the Slashtel eSIM as your default line for data. That way your home number stays reachable for OTPs and calls, while all your internet runs on the eSIM and you are not billed for data roaming.
Does the eSIM give me a local phone number?
No. Slashtel eSIMs are data only. They supply mobile internet in your destination but do not include a local number, calls or SMS. For staying reachable you use your existing home number, and for calls and messages most travellers use apps over the eSIM data.