Incorporating a telephone interconnect call mode of operation onto a trunked system has generally been constrained by the simplex (voice and data signaling) nature of trunked system subscriber units. Similarly, signaling and call processing by fixed-end control equipment is also simplex formatted. While the introduction of duplex voice/RF-capable subscriber units utilizing simplex data signaling with fixed-end control equipment improves the grade of uses interconnect service, their use restricts the amount of dynamic control and call status changes possible while processing a current, duplex voice-only call. Throughout the present specification, the term "simplex" is used in the same context as the term "2-way half-duplex" may be used, although the meaning is the same: capable of transmitting in either direction, but not in both directions simultaneously.