A method of processing signalling relating to a telephony session in a first telephony network, the telephony session involving a telephony device associated with a second telephony network, the method comprising: receiving (S5c, S6g) a first telephony session establishment message from a first telephony network node in the first telephony network, the first telephony session establishment message comprising a first telephony identifier as a called party identifier, the first telephony identifier being associated with the first telephony network; identifying (S5d, S6h) a second telephony identifier, the second telephony identifier being associated with the first telephony network and being different from the first telephony identifier; transmitting (S5e, S6i) a second telephony session establishment message to the first telephony network node, the second telephony session establishment message comprising the second telephony identifier as a telephony party identifier, whereby to enable call services to be provided in the first telephony network on the basis of the second telephony identifier; receiving (S5g, S6k) a third telephony session establishment message from the first telephony network node, the third telephony session establishment message comprising the second telephony identifier as a telephony party identifier; identifying (S5h, S61) a third telephony identifier using the second telephony identifier, the third telephony identifier being associated with the second telephony network; and transmitting (S5i, S6m) a fourth telephony session establishment message to the first telephony network node, the fourth telephony session establishment message comprising the third telephony identifier as a telephony party identifier, wherein the method is performed by a second node in the first telephony network, wherein the first telephony network is a non-home network of the telephony device, and wherein the second telephony network is a home network of the telephony device. receiving (S5c, S6g) a first telephony session establishment message from a first telephony network node in the first telephony network, the first telephony session establishment message comprising a first telephony identifier as a called party identifier, the first telephony identifier being associated with the first telephony network; identifying (S5d, S6h) a second telephony identifier, the second telephony identifier being associated with the first telephony network and being different from the first telephony identifier; transmitting (S5e, S6i) a second telephony session establishment message to the first telephony network node, the second telephony session establishment message comprising the second telephony identifier as a telephony party identifier, whereby to enable call services to be provided in the first telephony network on the basis of the second telephony identifier; receiving (S5g, S6k) a third telephony session establishment message from the first telephony network node, the third telephony session establishment message comprising the second telephony identifier as a telephony party identifier; identifying (S5h, S61) a third telephony identifier using the second telephony identifier, the third telephony identifier being associated with the second telephony network; and transmitting (S5i, S6m) a fourth telephony session establishment message to the first telephony network node, the fourth telephony session establishment message comprising the third telephony identifier as a telephony party identifier, wherein the method is performed by a second node in the first telephony network, wherein the first telephony network is a non-home network of the telephony device, and wherein the second telephony network is a home network of the telephony device.