How to Configure a Travel eSIM with Apple Messages to Avoid Missing iMessages While Abroad

When traveling internationally with my iPhone, I often purchase a third party eSIM for data. In the past, before leaving the United States, I’ve made the mistake of disabling my primary line to avoid international cellular data overages. However, this has resulted in missed messages sent to my phone number while I'm away and a flood of missed messages upon my return. I’ve finally figured out why this happens and found a way to avoid using my primary line for data while traveling abroad. I can also receive iMessages sent to my primary phone number while using an eSIM abroad.

My understanding is that disabling my primary line in my home country deactivates my phone number registered with iMessage, and in my case, my phone number can only be re-registered with iMessage when I re-enable my primary line and reconnect to my carrier in my home country. The trick seems to be to keep my primary line active but disable data roaming, set the data plan to my travel eSIM and disable carrier switching.

To receive inbound messages in iMessage sent to your primary phone number and to make and receive phone calls over Wi-Fi while abroad using a data eSIM without incurring data overages on your primary line, follow these steps.

Before Leaving Home Country

Keep your primary line enabled DO NOT DISABLE IT however…

• To prevent international cellular data use while abroad disable data roaming on your primary line in Settings > Cellular > Primary
• To prevent accidental cellular data use on your primary line while roaming abroad disable cellular data switching in Settings > Cellular > Cellular data
• To allow Wi-Fi calling on your primary line while abroad you must enable “Wi-Fi Calling on This iPhone” before leaving your home country in Settings > Cellular > Primary > Wi-Fi Calling
• To use Wi-Fi Calling when you connect to Wi-Fi abroad using your primary line you must enable "Prefer Wifi When Roaming" in Settings > Cellular > Primary > Wi-Fi Calling
• To prevent accidental costs abroad from sending SMS messages disable SMS in Settings > Messages turn off 'Send as SMS' 

Upon Arriving in New Country 

• Enable your new eSIM (by scanning a QR code, etc) this often requires being on Wi-Fi
• To use your international cellular data plan enable cellular data access in Settings > Cellular Data >  select the name of your Travel eSIM (your primary network must NOT be selected)
• To use data roaming on your international data plan enable Data Roaming in Settings > Cellular >  select the name of your Travel eSIM 

Upon Returning Home

• Enable data roaming on your primary line in Settings > Cellular > Primary
• Enable SMS sending in Settings > Messages turn on 'Send as SMS' 
• Delete secondary line in Settings > Cellular > name of your Travel eSIM