I have configured DISA/Auto-Attendent (press 1 for sales, press 2 for
john, etc), and each selection rings a different group. So far, so
good.

The problem is that if the caller does not make a selection, which is
often the case when the call originates from a telemarketers
autodialer, the TD308 defaults to ring all extensions. This is exactly
the opposite of what I want. I want the system to drop the call, or
route it to an extension/jack that does is not currently in use, so
that no phone actually rings.

How can I program the TD308 to do this? Please provide complete set of
programming steps.

Too much information to sift through for just $5.00, but you can find
a manual for this phone here:

http://www.pasc.panasonic.com/OperatingManuals/KXTD308.PDF

You may already have this reference. If not, it has sections on USer
and Station programming.

Thanks.

Don't sift through the info.

Simply outline the steps to program DISA, indicating how to handle the
default case where no option is selected by caller.