System for managing access by a plurality of communication networks (20, 21, 22) to a mobile terminal connected to a mobile telecommunication network, characterized in that said system has at least - an application server that is capable of: ° transmitting a first control message with a user identifier to a domain name server and then to a user address search interface, ∘ receiving a network address of a user address search interface by means of a domain name server and ° setting up a connection from one of said communication networks (20, 21, 22) to said mobile terminal, - a user address search interface that is capable of assigning a user address to an incoming call management interface and of receiving the user address and a network address of an incoming call management interface, - an incoming call management interface that is capable of: ° checking the existence of the user address, ° when said user address does not exist, transmitting a third control message to an access control interface by means of a network address allocation server and, ∘ when the mobile terminal is accessible and has rights concerning the sending of an incoming call from said network, transmitting a fifth control message with the user address to the network address allocation server and of transmitting the user address and the network address to the user address search interface, - an access control interface that is capable of transmitting a fourth control message to an access authorization interface, - an access authorization interface that is capable of checking the accessibility and the rights of the user of said mobile terminal concerning the sending of an incoming call from said communication network with the location register, - a network address allocation server that is capable of assigning a network address and of transmitting the network address to the incoming call management interface. - an application server that is capable of: ° transmitting a first control message with a user identifier to a domain name server and then to a user address search interface, ∘ receiving a network address of a user address search interface by means of a domain name server and ° setting up a connection from one of said communication networks (20, 21, 22) to said mobile terminal, ° transmitting a first control message with a user identifier to a domain name server and then to a user address search interface, ∘ receiving a network address of a user address search interface by means of a domain name server and ° setting up a connection from one of said communication networks (20, 21, 22) to said mobile terminal, - a user address search interface that is capable of assigning a user address to an incoming call management interface and of receiving the user address and a network address of an incoming call management interface, - an incoming call management interface that is capable of: ° checking the existence of the user address, ° when said user address does not exist, transmitting a third control message to an access control interface by means of a network address allocation server and, ∘ when the mobile terminal is accessible and has rights concerning the sending of an incoming call from said network, transmitting a fifth control message with the user address to the network address allocation server and of transmitting the user address and the network address to the user address search interface, ° checking the existence of the user address, ° when said user address does not exist, transmitting a third control message to an access control interface by means of a network address allocation server and, ∘ when the mobile terminal is accessible and has rights concerning the sending of an incoming call from said network, transmitting a fifth control message with the user address to the network address allocation server and of transmitting the user address and the network address to the user address search interface, - an access control interface that is capable of transmitting a fourth control message to an access authorization interface, - an access authorization interface that is capable of checking the accessibility and the rights of the user of said mobile terminal concerning the sending of an incoming call from said communication network with the location register, - a network address allocation server that is capable of assigning a network address and of transmitting the network address to the incoming call management interface.