I had that on mine when I was running 4.3, but only with wifi calling. first random incoming calls, then all incoming calls would go straight into voice mail and then I couldn't even call out on wifi. Temporary solution was to change preferences to cellular calling from wifi calling. Then I updated to 4.4.2 (nf4) and its fixed now and it works fine with wifi calling and all. I suspected t-mo made some changes in their server software and either accidently or on purpose never tested properly with older firmware, introducing some bug, but feel free to call it wrong guess. The reason I suspected problem was on their side, was that I have not updated or changed my phone at all, since before problem started and installed probably only 1 new program, which later I deleted it as first suspect, but deleting it didn't fix the problem at all.