A method for establishing a 
multimedia session between a calling 
telecommunications equipment and a called equipment that is a mobile equipment of a network of the 
multimedia sub-domain type, wherein: an invitation (Invite) is sent from the first 
user equipment (UE1) to establish a 
multimedia session, which comprises as he destination address a public identity of the second equipment, said invitation being transmitted: by the first equipment (UE1) to a first 
proxy server (P-CSCF1), then, from this first 
proxy server, to a first 
session control server (S-CSCF1) of the network in which the first equipment (UE1) is registered, and from this first session 
server (S-CSCF1) to a 
point of entry server (I-CSCF2) of the network corresponding to the destination address of the second equipment (UE2); this 
point of entry server (I-CSCF2) interrogates a 
database (HSS2) of the network of the second equipment (UE2) in order to obtain the address of a 
session control server (S-CSF2) responsible for said second equipment (UE2); when said second equipment (UE2) is registered in said 
database: said 
point of entry server (I-CSCF2) transmits the invitation message to the selected session server (S-CSCF2), and said session server (S-CSCF2) transmits the invitation message to a 
proxy server (P-CSCF2) corresponding to the second equipment, wherein the proxy server (P-CSCF2) transmits this invitation message by encapsulating it in an IP packet to the second equipment via an appropriate transit node (GGSN).