A method performed by a network unit (104, 300), the method comprising: receiving a first request to establish an internet protocol multimedia subsystem, IMS, session with a user equipment, UE, (102, 702), wherein the UE (102, 702) is dual registered to: a first network access supporting fifth generation, 5G, core network connectivity; and a second network access supporting evolved packet core, EPC, network connectivity and circuit switched network connectivity, wherein the UE (102, 702) has connectivity to an IMS via the first network access or the second network access; determining first information corresponding to a network access connectivity selected from the first network access and the second network access, wherein the UE (102, 702) has internet protocol connectivity with the IMS through the network access connectivity; and transmitting a second request to a first network function to retrieve second information corresponding to voice support over packet switched connectivity over the IMS from the network access connectivity, wherein the second request comprises information indicating a second network function which is to be contacted by the first network function to retrieve the second information; wherein the second information indicates whether the first request is to be received via the network access connectivity via circuit switched connectivity or packet switched connectivity; wherein the first network function comprises a home subscriber server, HSS, or a unified data management function, UDM; and wherein the second network function comprises a mobility management entity, MME, or an access and mobility management function, AMF. receiving a first request to establish an internet protocol multimedia subsystem, IMS, session with a user equipment, UE, (102, 702), wherein the UE (102, 702) is dual registered to: a first network access supporting fifth generation, 5G, core network connectivity; and a second network access supporting evolved packet core, EPC, network connectivity and circuit switched network connectivity, a first network access supporting fifth generation, 5G, core network connectivity; and a second network access supporting evolved packet core, EPC, network connectivity and circuit switched network connectivity, wherein the UE (102, 702) has connectivity to an IMS via the first network access or the second network access; determining first information corresponding to a network access connectivity selected from the first network access and the second network access, wherein the UE (102, 702) has internet protocol connectivity with the IMS through the network access connectivity; and transmitting a second request to a first network function to retrieve second information corresponding to voice support over packet switched connectivity over the IMS from the network access connectivity, wherein the second request comprises information indicating a second network function which is to be contacted by the first network function to retrieve the second information; wherein the second information indicates whether the first request is to be received via the network access connectivity via circuit switched connectivity or packet switched connectivity; wherein the first network function comprises a home subscriber server, HSS, or a unified data management function, UDM; and wherein the second network function comprises a mobility management entity, MME, or an access and mobility management function, AMF.