I believe the "Record Beep Length" property under HKLM\Software\Active Voice\MIU\1.0\Initalization\ is used for the dialogic record beep call - yes, their board actually generates the beep (i.e. we don't play a wav file for the beep as we do for CM).
The value is 200 ms by default - however be careful cranking it out too far because while the board is generating this tone it's "blind" to incoming DTMF which means you could potentially miss a disconnect signal or the like - I'm suprised folks would be complaining about it not being long enough, actually, it's pretty noticable.
You can also fiddle with the "Record Beep Amp" value in the same branch, this is -17 db by default I believe (it's stored in hex where ffffffe is -1, fffffffd is -2 and so on). I've never touched this one before, however, so I'm unsure if that'll make the dialogic record beep louder or not, might be worth a shot.
I have no idea if these values are read only at Unity startup time or if they're referenced each time needed (I suspect at startup time only) - so you may need to restart Unity before they'll take effect.
