As of the firmware update version 412 all Circle headsets featuring call control now also feature the ability to use the EU limiter functionality.
In order to activate the EU limiter, simply press and hold the "Vol -" button for ten seconds.
To deactivate the EU limiter, press and hold the "Vol +" button for ten seconds.
The default setting if "off".
NOTE: There is no audible or visual cue for these settings.