Recently, I have discovered that sometimes, someone will call me and will hear my phone ring on their end and it takes them to my voice mail and I'm none the wiser. Most recent, I had someone call and leave a voice message 2 days ago and the voice mail symbol didn't show up until someone else left a second voice mail, so not only did I not know they had called but I didn't know someone had left a message either.
Another member of my household has the Thunderbolt as well and we have tested this, and numerous times when I call their phone and we're sitting right next to each other the person calling hears it ringing but the one receiving the call never knows they missed a call. We have both had our phones for a year and a half exactly.
What is causing this issue? How can we fix it?