One or more Internet Protocol, IP, Multimedia Subsystem, IMS, devices comprising: one or more processors; and memory storing instructions that, when executed by the one or more processors, cause the one or more devices to: establish a security association for a mobile device using a first Internet Protocol, IP, address associated with the mobile device; establish IP Multimedia Subsystem, IMS, session for the mobile device using the security association, the IMS session enabling secure network communications between the mobile device and an end-point device over an access network and an IMS network; responsive (408, 410) to a connectivity interruption that disables the secure network communications between the mobile device and the end-point device via the IMS session, receive credentials from the mobile device, the credentials comprising subscriber identity module, SIM, credentials; establish a new security association for the mobile device using a second IP address associated with the mobile device and the credentials received from the mobile device; use (414, 416) the SIM credentials received from the mobile device to determine that the mobile device was a participant in the IMS session prior to the connectivity interruption and that the IMS session is an active IMS session in the IMS network, the using the SIM credentials to determine that the mobile device was the participant in the IMS session prior to the connectivity interruption comprising matching the SIM credentials received with previous SIM credentials received from the mobile device in association with establishing the security association; and associate (418, 420) the new security association with the active IMS session so that the mobile device is capable of continuing the secure network communications with the end-point device. one or more processors; and memory storing instructions that, when executed by the one or more processors, cause the one or more devices to: establish a security association for a mobile device using a first Internet Protocol, IP, address associated with the mobile device; establish IP Multimedia Subsystem, IMS, session for the mobile device using the security association, the IMS session enabling secure network communications between the mobile device and an end-point device over an access network and an IMS network; responsive (408, 410) to a connectivity interruption that disables the secure network communications between the mobile device and the end-point device via the IMS session, receive credentials from the mobile device, the credentials comprising subscriber identity module, SIM, credentials; establish a new security association for the mobile device using a second IP address associated with the mobile device and the credentials received from the mobile device; use (414, 416) the SIM credentials received from the mobile device to determine that the mobile device was a participant in the IMS session prior to the connectivity interruption and that the IMS session is an active IMS session in the IMS network, the using the SIM credentials to determine that the mobile device was the participant in the IMS session prior to the connectivity interruption comprising matching the SIM credentials received with previous SIM credentials received from the mobile device in association with establishing the security association; and associate (418, 420) the new security association with the active IMS session so that the mobile device is capable of continuing the secure network communications with the end-point device. establish a security association for a mobile device using a first Internet Protocol, IP, address associated with the mobile device; establish IP Multimedia Subsystem, IMS, session for the mobile device using the security association, the IMS session enabling secure network communications between the mobile device and an end-point device over an access network and an IMS network; responsive (408, 410) to a connectivity interruption that disables the secure network communications between the mobile device and the end-point device via the IMS session, receive credentials from the mobile device, the credentials comprising subscriber identity module, SIM, credentials; establish a new security association for the mobile device using a second IP address associated with the mobile device and the credentials received from the mobile device; use (414, 416) the SIM credentials received from the mobile device to determine that the mobile device was a participant in the IMS session prior to the connectivity interruption and that the IMS session is an active IMS session in the IMS network, the using the SIM credentials to determine that the mobile device was the participant in the IMS session prior to the connectivity interruption comprising matching the SIM credentials received with previous SIM credentials received from the mobile device in association with establishing the security association; and associate (418, 420) the new security association with the active IMS session so that the mobile device is capable of continuing the secure network communications with the end-point device.