There are many systems that are running voice over 2400 to 9600 Baud
lines using special compression chips.  At 2400 with some of the new
compression techniques they don't sound too bad, but I wouldn't pipe in
music while on hold :-)
Steve

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E-mail: sdavidson@its.bldrdoc.gov
Steven Davidson
Dept. of Comm.  NTIA-ITS.N2
325 Broadway
Boulder, CO  80303
W 303-497-3411  FAX 5995
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