Hello list,
My friend recently posed this question to me.  I came up with an answer,
but am sure there is a much better explanation to be given for a remedy
to his situation.

/*

We are getting an IP-based phone system that will primarily be used
internally dues to bandwidth issues.  this will take about 60-90 kbps.
our
current internet access plan is 128k up, 256k down.  it will be enough,
but
as soon as someone starts doing anything on the internet, our phone
calls
will probably go to crap.  now m0n0wall has a traffic shaper that can
fix
this, but my question is can a traffic shaper rule be demand-based?  can
90k
of upstream traffic be reserved only when a phone call is happening and
not
fulltime?  just wondering.

jorj

*/

I told him that this was probably possible but not through the gui. This
answer may be quite incorrect, so I'm posting it here yearning for some
more professional insight.

Thanks in advance,
--Michael I.