Are voice and data transmitted differently?
3G (UMTS): Yes.
4G (LTE): No.
3G (UMTS): At the access layer, voice and data are transmitted similarly over the UTRAN. At the core layer, voice is transmitted over a circuit-switched core via SS7 to the PSTN, and data is transmitted over a packet-switched core to the IP network (e.g. Internet).
4G (LTE): Both voice and data are transmitted similarly through access layer through the E-UTRAN and EPC, which replaces both PS core and CS core of 3G. Only at the last leg, where the traffic exits the EPC, does the traffic diverge. Voice traffic is routed through CSCFs into the IMS core, and data traffic is routed through the PGW to the IP network (e.g. Internet).
UMTS: Universal Mobile Telecommunications System
UTRAN: UMTS Terrestrial Radio Access Network
SS7: Signalling System 7, the standard for signalling and switching telephone calls
PSTN: Public Service Telephone Network, the global network of interconnected telephone network operators
LTE: Long-Term Evolution
E-UTRAN: Evolved UTRAN
EPC: Evolved Packet Core