Evening all. I have a problem with my girlfriend's iPhone 6 and I'm somewhat baffled. When she is making a voice call fairly regularly the call will drop and the phone will display No Service even if she's in an area with full signal. In order to rectify the problem we've done the following, in this order: 1) We reset the network settings, 2) Restored the software 3) Contacted EE who did some sort of 'refresh' 4) Replaced the iPhone at the Apple Store 5) Replaced the Sim Card. None of these have worked - the problem continues to persist. Any ideas please?