OpenSky
From The RadioReference Wiki
OpenSky is M/A-COM's implementation of AMBE digital modulation over a TDMA channel format.
AMBE is another vocoder developed by DVSI Inc. Operation is very similar to Nextel TDMA digital voice systems.
OpenSky systems do not use a control channel.
Like ProVoice Open Sky cannot be monitored by any scanner, past or future.
OpenSky technology is owned by M/A-COM, Inc. a unit of Tyco Electronics
Here is the MA Com link for this product