A method of managing fixed and mobile terminals in an environment comprising a mobile network including an IMS network, and an enterprise network including IP-PBX equipment, the method consisting in particular in: determining (S30) the mobile terminals of the mobile network that are registered with the IMS network and the enterprise terminals that are registered with the IP-PBX equipment of the enterprise network; while a multimedia communications session involving any terminal that is determined as being registered with the IMS network or with the IP-PBX equipment as the case may be, is being initialized via the IMS network, obtaining (S32) the capabilities of said terminal; and updating (S31, S33) a database with information identifying the mobile terminals of the mobile network that are registered with the IMS network and the enterprise terminals that are registered with the IP-PBX equipment, and with information representative of the capabilities that have been obtained for each identified terminal.