Network operators around the world are looking to start providing voice calls over their LTE networks via VoLTE technology (voice over LTE), though by default, VoLTE doesn't allow switching voice calls to 3G networks when the need arises, such as in areas where the operator's LTE network isn't available, which means that if you lose your 4G network while on a call, the call will be disconnected instead of being switched over to the 3G network.
To counter this, Samsung has begun offering customers its Single Radio Voice Call Continuity (SRVCC) service, which can transfer (handover) calls from VoLTE to 3G (WCDMA), allowing a call to continue uninterrupted even if you lose LTE coverage. SRVCC will be helpful to operators in the early stages of VoLTE deployment, as that's the time when network availability will be scarce.
SRVCC is now available to customers in South Korea, and the first device to support it will be the LTE-A variant of the Galaxy S4 in the country, with devices using Samsung's SHANNON222 modem chipset getting compatibility initially.
