Something's definitely odd with this situation, perhaps specific to t-mobile. My housemate (pixel9 as well, also on t-mobile) had this issue for an hour and a half or so and after resetting the mobile settings, and powering down several times now can make calls - but when I call them the phone does not ring and goes straight to voicemail. I attempted to call them while they were on a call and was hung up on instead of being redirected to their voicemail. We reproduced these scenarios several times.