Does WhatsApp keep working with my number on a travel eSIM?
Short answer. Yes. WhatsApp is tied to your registered number, not to the SIM that supplies data, so it keeps working over the travel eSIM. Keep the home SIM in the phone in case WhatsApp asks you to verify again, which needs that SIM to receive an SMS or call.
What does WhatsApp say?
"If you use a local SIM card while traveling, you can still use WhatsApp with your home number. But if you need to re-verify your account, you can't do this on your original WhatsApp number." To verify, "you must have the corresponding SIM card in your device, with phone or SMS service enabled."
What should I avoid?
- Don't use Settings > Account > Change number unless you mean to move the account for good.
- Don't log out or reinstall WhatsApp abroad: that is what triggers re-verification.
- Don't remove the home SIM on a phone that only takes one physical SIM, unless you are sure you won't need a code.
Will it cost me roaming fees?
Not if data runs over the travel eSIM. Turn off data roaming on the home line; WhatsApp itself recommends turning off mobile data roaming if you don't have an international plan.