How your cellular provider charges you when you're abroad
Cellular providers can charge you for data usage, for voice calls and for SMS
If you have signed up for a "roam like home" plan with your provider (i.e., you pay $10/day to use your regular cellular plan abroad), your operator will charge you the full daily fee as soon as you:
use even 1 KB of data, make or receive a single phone call, or send even 1 SMS
Any activity (data, call or SMS) will initiate your 'daily' roam-like-home plan, whether you keep using it or not
You can have your 'data roaming' turned OFF for your Primary (regular) SIM card (which is always recommended), but the daily fees will still apply if you make or take a phone call on your regular phone number, or if you send an SMS while you're abroad
Receiving SMS is free of charge (for almost all providers) even if you're abroad
If you do not have a "roam like home" plan (or any other specific roaming plan) it could be even more costly on your travels -as your operator will charge you 'full rates' based on your data, call and SMS usage
Recommended Settings for your Primary SIM to avoid Roaming Charges:
The safest, most guaranteed way to avoid any kind of roaming charges from your regular operator when you are abroad is to turn OFF your regular (primary) SIM card on your device until you're back home.
You can use your Roamless eSIM for data connectivity, and use Whatsapp, iMessage, Facetime, Messenger and other messaging apps to text and make voice and video calls.
If you keep your primary SIM card turned OFF:
You will not be able to receive any phone calls on your regular phone number
You will not be able to receive any SMS messages (e.g., 2FA codes from your bank)
You cannot not be charged by your primary provider
If you decide to keep your Primary SIM card ON, please make sure to:
Turn 'data roaming' OFF for your Primary SIM (to ensure your device cannot use your regular SIM for data connectivity while abroad, even by mistake)
Not answer any incoming calls on your regular phone number
Not make any calls using your regular SIM card (i.e., your device's phone app)
Not send any SMS messages
You can use Roamless in-app calling feature to call back the number for the missed call if you wish.
Receiving SMS is free (on most providers), so you can get your one-time passwords and codes (e.g., from your bank) without incurring any roaming charges
Note: Once you're back home, remember to turn off your Roamless eSIM and turn on your Regular (Primary) SIM.