I'm running a Netbsd 1_1_Alpha Kernel on an i386 @ 20Mhz.  The serial port
is a Hayes ESP card, which works flawlessly.

The other day I wanted to make ppp redial, so I just flipped power to the
external modem off.  The machine responded by locking solid.  No errors,
no pings, no disk activity, no network activity; required punching the reset
button.  This is the sort of thing I used to see when I was using SLIP and
a set of nasty scripts to bring up and maintain the slip line.

If you have an external modem, how about flicking it off while its doing
ppp or slip (or even terminal use) and posting your results?

-john