Commenting here just to keep the thread going. This has been happening to me for about a year now. I thought it was my previous iPhone, switched to the new 15, and same thing happens. I also have T-Mobile, and as someone that will be on a long phone call for work, it starts to drive me crazy after a while. I had previously contacted Apple support, and their suggestion was to try switching carriers, but based on this thread that I finally found, it's good to know I'm not alone, I'm not going crazy, and that it is fairly easy to trace back to T-Mobile. This needs to be fixed. If I didn't get such a good deal with T-Mobile, I would happily leave.