VoIP is increasingly used in voice communication systems, where integration of legacy radios is an important feature. In addition to managing radio channel access, requiring Push-to-Talk (PTT) and Squelch signals, also cross coupling of radio channels is an important feature in air traffic control and public safety applications. Therefore we present a signaling approach based on the Session Initiation Protocol (SIP) in combination with a dynamic master slave model. It provides compatibility with standard SIP-phones and the existing expiry mechanism is used for detection of failure states. We complete our contribution with estimations of the audio and PTT-request delay in a coupled sector.