If you select “Off,” your iPhone will rely on 3G or slower cellular networks for voice and data. If you select “Voice & Data,” your iPhone will use the fastest available LTE networks for both voice and data. Use of LTE improves the quality of voice and data connections over cellular networks. If you select “Data Only,” your iPhone will use LTE for data, and to access the Internet, but voice calls will utilize slower cellular networks.
If you select 3G, your iPhone will rely on 3G cellular networks for voice and data, when available. If you select 2G, your iPhone will rely on 2G cellular networks for voice and data, when available.
