Many years ago ATT (I think) did a study to determine how long an
on-going voice telephone call would continue.  It turned out the best
predictor of future duration was past duration.  For example, if a
call has been going on for one minute, the most likely future duration
is one minute. If it's been going on for an hour, the most likely
future duration is one hour.

I would like to find that study.  That is, I'd like to read the
detailed results.

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Clarification of Question by wardtalktothebeaver-ga on 28 Jan 2003 02:21 PST

I don't believe the study relates to "call holding time".  I couldn't
determine exactly what call holding time is, but it seems to relate to
the time a call is waiting to be handled.  The question relates to an
actual conversation that is in process.  The citations reflected in
the first comment seem not to relate to voice calls but rather to data
calls.  It may be, however, that one of the statistical distributions
cited does, in fact, fit the data for voice calls as well.

Hi,

I came across the following survey although I couldn't get hold of a
hard copy of the report:

V. Bolotin., "Telephone Circuit Holding Time Distributions", Proc.
14th ITC, Elsevier Science B.V. pp. 125-134, 1994

Is this what you were looking for? You can also read in what context
this report was cited at:

http://citeseer.nj.nec.com/context/287597/0

Regards.