Am on iPhone 5 (6.1.4 OS and MTN Carrier 14.1).
I am now getting similar problems regularly:
"No Service" comes and goes sometimes three times a day, sometimes fine for three days
People call me, phone doesn't ring
People leave voicemail, I get no notification then suddenly on Thursday I'll get notified of 5 "new" voicemails dating back to Monday
Live in paarl so unlikely LTE but will try with it off