A communication device for connecting a first user device, said user device authenticating and authorizing to a first core network, with a second core network for connecting to a public network, the communication device comprising: a first database storing a plurality of first user profiles including one or more user specific numbers and one or more address names of the communication device assigned to each user specific number; a second database storing a plurality of second user and network specific information including a user specific number, an address name of the communication device and the addresses and address names of second core networks; first signalling means to enable signalling between the first user device and the first database; a GTP proxy controller, GPC , wherein the communication device is configured to, upon receipt of a first request message at the first database, send a first response message to the first core network and; the GPC is configured to receive a second request message from the first core network, the second request message including a user specific number and an address name of the communication device, and being a session request message, wherein the GPC is configured to terminate the second request message and to set up a new session request message as third request message to a second core network, wherein the GPC is configured to identify the second core network from a plurality of core networks by matching the address name of the communication device included in the second request message to one of the plurality of second user and network specific information stored in the second database, wherein the communication device is configured to establish a connection with the second core network by sending the third request message to the second core network, wherein after the establishment of the connection, the GPC is configured to route data of the first user device from the first core network to the second core network. a first database storing a plurality of first user profiles including one or more user specific numbers and one or more address names of the communication device assigned to each user specific number; a second database storing a plurality of second user and network specific information including a user specific number, an address name of the communication device and the addresses and address names of second core networks; first signalling means to enable signalling between the first user device and the first database; a GTP proxy controller, GPC , wherein the communication device is configured to, upon receipt of a first request message at the first database, send a first response message to the first core network and; the GPC is configured to receive a second request message from the first core network, the second request message including a user specific number and an address name of the communication device, and being a session request message, wherein the GPC is configured to terminate the second request message and to set up a new session request message as third request message to a second core network, wherein the GPC is configured to identify the second core network from a plurality of core networks by matching the address name of the communication device included in the second request message to one of the plurality of second user and network specific information stored in the second database, wherein the communication device is configured to establish a connection with the second core network by sending the third request message to the second core network, wherein after the establishment of the connection, the GPC is configured to route data of the first user device from the first core network to the second core network. <EOS>