Originally Posted by LarryJ

They are adding it to the 737 fleet at a good clip. Quite a few of them are now equipped.

There's no way for you to tell if the system is active on the 737s. Having the menu item isn't enough. They have to make a modification to change the Ch.9 audio source from the Observer's audio panel to the #1 Comm radio. The only way to tell if that's been done, and the system activated, is to look at the switch in the cockpit and see if the "INOP" placard has been removed.