I have an unlocked M8 on At&t. My boss saw it and went and got a new M8 on Verizon. He's having an issue that I just can't figure out. Here's the story - He was on At&t using a Galaxy S4, switched to Verizon, ported his number and got an M8. When he is at home and connected to his wifi and gets a call from his girlfriend (also on Verizon) the phone will not ring, the call goes straight to voicemail, he gets the VM notification and message but no missed call. If his son calls under the same conditions (son is on At&t) the call is received normally, phone rings and can be answered. If he switches off wifi and his girlfriend calls, the phone rings and the call is connected normally. He's already been back to the Verizon store and they gave him a new sim card. I know this sounds weird but anyone have an idea what is causing this issue? Any help would be appreciated. Verizon employees at the store have no clue what may be the problem.