Gentlemen:

Bob Reise says.....

Make sure that you dont have anyone calling you when the phone line is
connected to
your computer as ring voltages can be as high at 140 volts AC

The AC is not 60 Cycle, it is 1000 Hz or a variant near by.  There are also
coded ringing systems that use different AC some as low as 850 Hz and some
as high as 1150 Hz or maybe more.  The peak AC voltage is 1.414 of the 120V
Battery.

ALSO

if you have ISDN (2B1Q coding)you will have up to 240 Volts DC, + 120
and -120 from tip to ring.  These voltages will also occur on some of the
ADSL and HDSL systems, where the terminal is line powered.  This means the
terminal in the home/business is powered from the Central Office.  These
voltages are not insignificant and can give you a real poke.

The 8 kHz to a power of n is interesting.  Note that many of the telco's now
TRANSCODE the regular 64 KBPS, which is really 56 KBPS into two 32 KBPS in a
64 KBPS as well as 16 KBPS for 4 in a 64 KBPS and some private line stuff is
actually 8 KBPS for 8 channels in a real 64 KBPS.  Now you know how those
really cheap LD carriers make their economics work hi.  You can hear in
North America the T1 internal line rates as far as a mile from a cable
carrying the old DC pair systems.

I know the 30 channel European system is different, completely different,
and much of the pairs in the UK are a 4 wire quad that is exceedingly
difficult to get much bit rate out of it because of the way they are twisted
together.

Larry
VA3LK