A network gateway receives a voice over long term evolution (VoLTE) call establishment request from an internet protocol (IP) multimedia services (IMS) core network for a mobile device. The network gateway queries a serving gateway to determine whether the mobile device is transitioning from a first evolved node B (eNB) to a second eNB. If the mobile device is transitioning, based on the existence of a user plane modify request, the network gateway delays forwarding the received request to a mobility management entity until the serving gateway informs the network gateway that the serving gateway received a first data packet from the mobile device via the second eNB as an indication the transition is complete.