A secure communications system (501) including a local digital terminal (510) coupled to an interworking function (538). The interworking function (538) couples the digital radio network (121) to a PSTN (542, 546, 548) and a remote analog communication terminal (552). The system (501) includes a novel method of establishing and end-to-end communication channel between local digital (510) and remote analog (552) terminals wherein the local digital terminal (510) establishes a direct digital channel (121) between itself (510) and the interworking function (538) and transmits a message describing its signaling capabilities to the interworking function (538). The interworking function (538) then trains its modem with the modem of the remote analog terminal (552) such that signaling capabilites of the local digital terminal (510) and the remote analog terminal (552) are not violated. Moving modem training procedures to interworking function (538) do not adversely affect establishing end-to-end communication channels.
