Discontinued by GN Netcom.  Look at the Plantronics PTT version instead: Plantronics SHS1890-15 6-wire Push-to-Talk Amplifier 

This is the GN Netcom 0911 dispatch push to talk (PTT) 6-wire amplifier. This PTT amplifier offers radio communication for 911/emergency applications. This amplifier is compatible with any GN Netcom headset. 

Key Features:

• 6-wire dispatch amplifier for PTT 911 environments
• Rotary volume control
• Non-locking push-to-talk button
• Belt clip
• GN Netcom headsets sold separately