While CS Fallback is operating as expected in routing voice calls to the 3G network - there are some short comings to the approach. When a subscriber on the LTE network makes or receives a voice call, the network redirects the device to the 3G network, where the voice call is attempted. Upon completion of the voice call and any active data session, the device must re-select the LTE network. An unintended consequence is that if an LTE subscriber is using an application (e.g. Facebook) on the 4G network at the time of the call, both the voice and data session are moved back to the 3G network. Until the data session is completed or the device is reset, the subscriber will camp on the 3G network. Subscribers may be \'disappointed by their supposed "˜4G' service which is actually being delivered through the operator's legacy 3G infrastructure.
The 4G network assets may be underutilised as more subscribers than expected will fallback and stay on the 3G network. While the migration to 4G is meant to alleviate capacity constraints on 3G networks, 4G subscribers camping on the network might cause blocks and access failures for subscribers with only 3G user equipment.