A method of performing signalling and media conversion in a multioperator (MN01, MN02, FN03, FN04) environment, the environment comprising at least a first network of a first network operator, a second network of a second network operator, and an IPX proxy, the method comprising: receiving in the IPX proxy, from a first client connected to the first network, a signalling message requesting a media flow establishment to a second client connected to the second network; detecting, by the IPX proxy, that the signalling message is targeted to the second network; fetching, by the IPX proxy, signalling and media flow specification information of the second network from its database, the specification information comprising one or more features; sending, by the IPX proxy, a request for additional feature information to the second network or to the second client in the second network; receiving the requested feature information; carrying out, by the IPX proxy, at least one conversion to the received signalling message using the fetched and received signalling features of the second network so that the signalling message is after conversion according to the signalling features of the second network; transmitting, after the at least one conversion, the signalling message from the IPX proxy to the second network; receiving in the IPX proxy from the second network an acceptance of the second client to establish the media flow between the first client and the second client; transmitting the acceptance from the IPX proxy to the first network; receiving in the proxy the media flow from the first network; comparing, by the IPX proxy, features of the media flow with corresponding media flow features of the second network; if one or more features of the media flow are different from one or more corresponding media flow features of the second network, carrying out, by the IPX proxy, at least one conversion to the received media flow on the basis of the different one or more features so that the media flow is after conversion according to the media flow features of the second network; transferring the media flow from the proxy to the second network; establishing, after transferring the media flow to the second network, the connection between the first client and the second client; wherein the conversions are transparent to the first network, the second network, the first client and the second client. receiving in the IPX proxy, from a first client connected to the first network, a signalling message requesting a media flow establishment to a second client connected to the second network; detecting, by the IPX proxy, that the signalling message is targeted to the second network; fetching, by the IPX proxy, signalling and media flow specification information of the second network from its database, the specification information comprising one or more features; sending, by the IPX proxy, a request for additional feature information to the second network or to the second client in the second network; receiving the requested feature information; carrying out, by the IPX proxy, at least one conversion to the received signalling message using the fetched and received signalling features of the second network so that the signalling message is after conversion according to the signalling features of the second network; transmitting, after the at least one conversion, the signalling message from the IPX proxy to the second network; receiving in the IPX proxy from the second network an acceptance of the second client to establish the media flow between the first client and the second client; transmitting the acceptance from the IPX proxy to the first network; receiving in the proxy the media flow from the first network; comparing, by the IPX proxy, features of the media flow with corresponding media flow features of the second network; if one or more features of the media flow are different from one or more corresponding media flow features of the second network, carrying out, by the IPX proxy, at least one conversion to the received media flow on the basis of the different one or more features so that the media flow is after conversion according to the media flow features of the second network; transferring the media flow from the proxy to the second network; establishing, after transferring the media flow to the second network, the connection between the first client and the second client; wherein the conversions are transparent to the first network, the second network, the first client and the second client.