I was having issues with my phone not ringing (LG volt) on boost network. I tried a factory reset, checked all my settings and it still would go straight to voicemail. After reading various post and I tried all the suggestions. I think I figured it out. I went to setting , more, mobile networks, under network mode and changed it from LTE/CDMA to CDMA only. This seems to have done the job. I don't know if it is carrier specific or coverage area specific but it is not a device problem. I am on android 4.4.2