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 (ID1) as a called party identifier, the first telephony identifier (ID1) being associated with the first telephony network ; identifying (S5d, S6h) a second telephony identifier (ID2), the second telephony identifier (ID2) being associated with the first telephony network and being different from the first telephony identifier (ID1); 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 (ID2) 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 (ID2); 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 (ID2) as a telephony party identifier; identifying (S5h, S61) a third telephony identifier (IDA) using the second telephony identifier (ID2), the third telephony identifier (IDA) 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 (IDA) 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 (ID1) as a called party identifier, the first telephony identifier (ID1) being associated with the first telephony network ; identifying (S5d, S6h) a second telephony identifier (ID2), the second telephony identifier (ID2) being associated with the first telephony network and being different from the first telephony identifier (ID1); 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 (ID2) 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 (ID2); 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 (ID2) as a telephony party identifier; identifying (S5h, S61) a third telephony identifier (IDA) using the second telephony identifier (ID2), the third telephony identifier (IDA) 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 (IDA) 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 . <EOS>