@MrT10001 I am having similar issues to the original poster. I use Google Fi service (the U.S.) and when I insert my sim card, I cannot make phone calls nor receive ones. I am not sure if I need to specifically configure my sim card (I just inserted it and restarted.)

Based on your comment, does it mean that if my Google Fi sim card only supports 4G, it will not work on my pixel 3a? If so, maybe I will get 3g sim card from Google Fi.
Thank you!