Any statistics from a reputable source (web site, book, gov stat.,
university) on average number of e-mail or total communications
received by field sales people from their own corporation.  Looking
for some measure of total volume of the information overload versus
the time to absorb it

How do you know they're experiencing "information overload " if you
don't know the volume of e-mails/calls yet?

Having been working in Corp America for 25 years I have watched the
volume of information continue to increase.  E-mail and the web have
only increased the volume.  Most of it not relevant or useful.  Junk
from outsiders plus junk from insiders.  Looking to quantify the
amount.  Does this help?