Who I have the same questioned this topic

Why does it switch from 4G to 1G when making or receiving calls. Works of 4G but the moment I answer or make a call it goes to 1G thru the duration of the call. When I hang up it goes back to 4G. I have a Galaxy Note 5 and never had this issue with my Galaxy S5. I have had this phone for a week now and it'seems doing the same to my boyfriends phone. I am at home on Wi-Fi and my network it's good.