CSFB
Circuit-Switched Fall-Back
A technology standard that allows separate LTE and CDMA wireless networks to interoperate, for seamless service with carrier companies that use both CDMA and LTE technology for their mobile networks. It allows LTE to be used as the primary network for data, with phones "falling back" to CDMA for voice calls and other circuit-switched services.
CSFB will eventually be replaced by VoLTE and related technologies.
See: VoLTE
