Lately, I've been suffering from this bug, where the call gets dropped. I tried doing a factory reset, a restore, a network settings reset, toggling airplane mode, etc. All these temporarily worked. It's running iOS 9.2, and I also contacted the Apple Store, and they gave me a volley of fixes. I tried them all, to no avail. They've in fact, suggested that I go to an Apple Authorized Service Centers to get my device replaced. Is it just me, or has anyone else had this issue? Please help me out here ...