OpenHandset puts the modem into a mode that will allow playing audio (wave files) to the handset.
CloseHandset resets the modem to class 0.
One or more command strings can be used.
HKR, OpenHandset, 1,, "at#cls=8"
HKR, OpenHandset, 2,, "at#vls=1"
HKR, CloseHandset, 1,, "at#cls=0"
These commands are used to play audio through the handset while there is no active call.