I didn't want to wait, so converted it to international:
Thread 'T-Mobile 6T to International Conversion (WITHOUT unlocked bootloader/SIM unlock!)' https://forum.xda-developers.com/t/t-mobile-6t-to-international-conversion-without-unlocked-bootloader-sim-unlock.3888307/
You can then unlock it without waiting.
I also purchased a dual sim tray for $6: https://www.amazon.com/dp/B07T1PTRJP/ref=cm_sw_r_cp_apa_glt_fabc_9WEXMBDNBJ8PH7NVVG32?_encoding=UTF8&psc=1