Hayelom Fessha ® on Twitter: "If you have a @TMobile 5G phone... it's important that you make sure you're using a new R15 SIM card to access all of our new network.
How to activate any T-Mobile SIM card - Android Authority
Quick and Easy Guide to Activate Your T-Mobile SIM - UnlockBase
NEW TMobile SIM 4G LTE OEM NANO Sim Card TRIPLE CUT SIM 3 IN 1. REPLACEMENT SIM | eBay
PSA: You need one small but very important thing to access T-Mobile's standalone 5G network - PhoneArena