A method comprising: intercepting (2-4, 3-4a), by an intermediary network element, a session invitation protocol invite message for setting up a communication from an originating operator (OP A, OP B, OP C, OP D) and targeted to a receiving operator (OP A, OP B, OP C, OP D) in a communications system; checking (2-4, 3-4b, 3-6, 3-7, 3-8), by the intermediary network element, whether the originating operator (OP A, OP B, OP C, OP D) and the receiving operator (OP A, OP B, OP C, OP D) use the same format of SIP (SIP, SIP-I, ISUP) for the SIP invite message; if the receiving operator (OP A, OP B, OP C, OP D) uses another format of SIP (SIP, SIP-I, ISUP) for the SIP invite message, performing (2-10, 3-10), by the intermediary network element, a conversion from the originating operator's (OP A, OP B, OP C, OP D) format of SIP (SIP, SIP-I, ISUP) to the receiving operator's (OP A, OP B, OP C, OP D) format of SIPl (SIP, SIP-I, ISUP) to produce a converted SIP invite message; forwarding (2-12, 2-14), by the intermediary network node, the SIP invite message towards an originally-addressed network node of the receiving operator (OP A, OP B, OP C, OP D), and the converted SIP invite message towards another network node of the receiving operator, whereby an interoperator interface stays the same for the originating operator; and forwarding, by the intermediary network node, a first part of the communication towards the originally-addressed network node of the receiving operator (OP A, OP B, OP C, OP D), and a second part of the communication towards the other network node of the receiving operator. intercepting (2-4, 3-4a), by an intermediary network element, a session invitation protocol invite message for setting up a communication from an originating operator (OP A, OP B, OP C, OP D) and targeted to a receiving operator (OP A, OP B, OP C, OP D) in a communications system; checking (2-4, 3-4b, 3-6, 3-7, 3-8), by the intermediary network element, whether the originating operator (OP A, OP B, OP C, OP D) and the receiving operator (OP A, OP B, OP C, OP D) use the same format of SIP (SIP, SIP-I, ISUP) for the SIP invite message; if the receiving operator (OP A, OP B, OP C, OP D) uses another format of SIP (SIP, SIP-I, ISUP) for the SIP invite message, performing (2-10, 3-10), by the intermediary network element, a conversion from the originating operator's (OP A, OP B, OP C, OP D) format of SIP (SIP, SIP-I, ISUP) to the receiving operator's (OP A, OP B, OP C, OP D) format of SIPl (SIP, SIP-I, ISUP) to produce a converted SIP invite message; forwarding (2-12, 2-14), by the intermediary network node, the SIP invite message towards an originally-addressed network node of the receiving operator (OP A, OP B, OP C, OP D), and the converted SIP invite message towards another network node of the receiving operator, whereby an interoperator interface stays the same for the originating operator; and forwarding, by the intermediary network node, a first part of the communication towards the originally-addressed network node of the receiving operator (OP A, OP B, OP C, OP D), and a second part of the communication towards the other network node of the receiving operator.