T-Mobil you don’t have to do anything.

I have an iPhone 13 plus with Verizon, most iPhones are now dual sim. So I have my US number as an E-sim and have the Chippie installed as a chip and can flip back and forth. Super easy and no need for a second phone. But to be honest I almost never used my sxm number as there is Wi-Fi everywhere. Keep you phone on “cellular data off”, you don’t incur charges but calls and texts will come in and respond when on Wi-Fi.