Originally Posted by draver

Anyone trying to activate a second esim on an iPhone 13X with T-Mobile will find it difficult if not impossible. I tried and failed several times and T-Force also could not get it to work. The self install off of the desktop app "Change Sim" reports the EID is already in use, Contact Support for help. I already had my primary voice line on esim, and Apple says this is a new feature that I certainly could use, so I did a little snooping.

What I discovered is a workaround that fools the system into believing your 2 esims are on two separate devices. This may only work with a second line on your TM account, but other carrier esims should install anyway. Put your TM second simcard in another esim iPhone. It will then register as a device on your account. Then on the device to install as an 2nd esim, open "Cellular", "Add Cellular Plan" and choose that number to transfer. iOS apparently is configured to transfer esims amongst devices and it only takes a few clicks to move that number to your preferred phone as a second esim. I assume it is registering the EID of the donor device to bypass the conflict.

Anyhoo, I now have 2 T-Mobile esims running in dual sim, dual standby mode, with my Verizon/Red Pocket in the sim slot as a fallback. Any 2 of the 3 lines can be active at the same time in either voice or data status. This is saving me from sim swaps and will be useful for international roaming with IMS simulated WiFi voice service. It allows me to keep my voice esim active with a cheap foreign data esim running also. Thank you Apple!