A wireless transmit/receive unit, WTRU, characterized by: a processor comprising a Non-Access Stratum, NAS, and an Access Stratum, AS,: wherein the NAS comprises a legacy Mobility Management, MM, unit and an Evolved Packet System, EPS, Mobility Management, EMM, unit, wherein the NAS is configured to determine whether to perform a Circuit Switched, CS, fallback based on an Internet Protocol, IP, Multimedia Subsystem, IMS, registration status, and wherein, responsive to determining to perform the CS fallback, the legacy MM unit is configured to notify the EMM unit of a CS call, and the EMM unit, in response to receiving the notification of the CS call, is configured to send, on a condition that the WTRU is attached to a CS domain, a CS service request indicating a request to perform the CS fallback; the AS is configured to receive the CS service request from the EMM unit, send an indication of the CS service request in a Radio Resource Control, RRC, message to an Evolved Universal Mobile Telecommunications System, UMTS, Terrestrial Radio Access Network, E-UTRAN, wherein the RRC message includes CS service information, and receive a handover command in response to the CS service request; and in response to receiving the handover command, the EMM unit is configured to receive from the AS an indication that the CS fallback has been performed and send an indication to the legacy MM unit that the WTRU is operating in the CS domain. a processor comprising a Non-Access Stratum, NAS, and an Access Stratum, AS,: wherein the NAS comprises a legacy Mobility Management, MM, unit and an Evolved Packet System, EPS, Mobility Management, EMM, unit, wherein the NAS is configured to determine whether to perform a Circuit Switched, CS, fallback based on an Internet Protocol, IP, Multimedia Subsystem, IMS, registration status, and wherein, responsive to determining to perform the CS fallback, the legacy MM unit is configured to notify the EMM unit of a CS call, and the EMM unit, in response to receiving the notification of the CS call, is configured to send, on a condition that the WTRU is attached to a CS domain, a CS service request indicating a request to perform the CS fallback; the AS is configured to receive the CS service request from the EMM unit, send an indication of the CS service request in a Radio Resource Control, RRC, message to an Evolved Universal Mobile Telecommunications System, UMTS, Terrestrial Radio Access Network, E-UTRAN, wherein the RRC message includes CS service information, and receive a handover command in response to the CS service request; and in response to receiving the handover command, the EMM unit is configured to receive from the AS an indication that the CS fallback has been performed and send an indication to the legacy MM unit that the WTRU is operating in the CS domain. wherein the NAS comprises a legacy Mobility Management, MM, unit and an Evolved Packet System, EPS, Mobility Management, EMM, unit, wherein the NAS is configured to determine whether to perform a Circuit Switched, CS, fallback based on an Internet Protocol, IP, Multimedia Subsystem, IMS, registration status, and wherein, responsive to determining to perform the CS fallback, the legacy MM unit is configured to notify the EMM unit of a CS call, and the EMM unit, in response to receiving the notification of the CS call, is configured to send, on a condition that the WTRU is attached to a CS domain, a CS service request indicating a request to perform the CS fallback; the AS is configured to receive the CS service request from the EMM unit, send an indication of the CS service request in a Radio Resource Control, RRC, message to an Evolved Universal Mobile Telecommunications System, UMTS, Terrestrial Radio Access Network, E-UTRAN, wherein the RRC message includes CS service information, and receive a handover command in response to the CS service request; and the legacy MM unit is configured to notify the EMM unit of a CS call, and the EMM unit, in response to receiving the notification of the CS call, is configured to send, on a condition that the WTRU is attached to a CS domain, a CS service request indicating a request to perform the CS fallback; receive the CS service request from the EMM unit, send an indication of the CS service request in a Radio Resource Control, RRC, message to an Evolved Universal Mobile Telecommunications System, UMTS, Terrestrial Radio Access Network, E-UTRAN, wherein the RRC message includes CS service information, and receive a handover command in response to the CS service request; and in response to receiving the handover command, the EMM unit is configured to receive from the AS an indication that the CS fallback has been performed and send an indication to the legacy MM unit that the WTRU is operating in the CS domain.