Originally Posted by TGarza

iPhone term is IMS, Google Pixel term is backup calling, Samsung S23 term is DSDV. The objective is to use your domestic sim over WiFi using the data of the 2nd local sim without international roaming charges. All 3 phones achieve the same result with different steps. At one time I travelled with 2 phones. One had a local sim with hotspot enabled and my other phone connecting using WiFi. Now some phones are capable of doing the same by adding a 2nd sim and changing some settings. My son in Europe called the US using his domestic number without incurring any charges other than his local data sim.

The iphone has to be unlocked, XR or newer, WiFi calling has to be enabled and the domestic sim is set to a non roaming partner or has data disabled. The sim is always active similar to airplane mode. Disabling the SIM interferes with calls and texting.


The iPhone domestic sim will use the data of the local sim with no international roaming charges. draver has been journaling his IMS travels using US Mobile and T Mobile international data. There is a Verizon plan which doesn’t work IMS. Some Australia/New Zealand providers have geo location restrictions for WiFi usage. Many US MVNO’s without international roaming work using IMS or one of the other options.


Hopefully others will add their comments since multiple users take advantage of this feature when traveling internationally. I have a work Google Pixel and can see the backup calling switch but I have not added a sim to test the functionality.