This first came into my attention about two weeks ago when I was waiting for scheduled calls from possible employers. So when the interviewer was trying to call me, they heard two tones and the call went straight to voice mail.
For an initial test, I asked my brother (same family plan) and a friend (different network) to call me immediately, the calls went through fine. This seemed like an isolated case here. I was receiving calls fine for most of that week.
However, soon afterwards I was missing calls from a wide range of people at different times of the day. Some were from people in my family plan so I was also able to match their call attempts on the T-Mobile website Usage log. But my phone didn't log these calls. They were consecutive attempts and none were logged on my phone.
On my end, I've had success calling people each time I've tried. And when I ask people to call me right back, the calls are seen by me. This has been a huge issue so far.
My phone is a good condition Samsung Galaxy S4 with the same service with T-Mobile I've had for years.