A method of wireless communication carried out by a user equipment, UE , comprising: performing an Internet Protocol, IP, Multimedia Subsystem, IMS, call over an untrusted Wireless Fidelity, Wi-Fi network by establishing a secure tunnel between the UE and a security gateway and registering with an IMS server using a first source IP address; connecting to the security gateway via a packet data network, PDN, gateway of a PDN, and a second access network which does not support IMS calls, the connecting comprising: sending a request to the security gateway using a multi-homing protocol over the PDN gateway, and receiving a response indicating a successful updating , by the security gateway , of a security association between the UE and the security gateway , in response to the request; and the method further comprising transferring the secure tunnel between the UE and the security gateway initially established over the untrusted Wi-Fi network to the PDN using the first source IP address to the second access network using a second source IP address; and transferring by the UE the IMS call from the first untrusted Wi-Fi network to the second access network, wherein the updating involves changing source IP address of the UE from the first source IP address to the second source IP address. performing an Internet Protocol, IP, Multimedia Subsystem, IMS, call over an untrusted Wireless Fidelity, Wi-Fi network by establishing a secure tunnel between the UE and a security gateway and registering with an IMS server using a first source IP address; connecting to the security gateway via a packet data network, PDN, gateway of a PDN, and a second access network which does not support IMS calls, the connecting comprising: sending a request to the security gateway using a multi-homing protocol over the PDN gateway, and receiving a response indicating a successful updating , by the security gateway , of a security association between the UE and the security gateway , in response to the request; and the method further comprising transferring the secure tunnel between the UE and the security gateway initially established over the untrusted Wi-Fi network to the PDN using the first source IP address to the second access network using a second source IP address; and transferring by the UE the IMS call from the first untrusted Wi-Fi network to the second access network, wherein the updating involves changing source IP address of the UE from the first source IP address to the second source IP address. sending a request to the security gateway using a multi-homing protocol over the PDN gateway, and receiving a response indicating a successful updating , by the security gateway , of a security association between the UE and the security gateway , in response to the request; and the method further comprising transferring the secure tunnel between the UE and the security gateway initially established over the untrusted Wi-Fi network to the PDN using the first source IP address to the second access network using a second source IP address; and transferring by the UE the IMS call from the first untrusted Wi-Fi network to the second access network, wherein the updating involves changing source IP address of the UE from the first source IP address to the second source IP address. <EOS>