🚀 go-pugleaf

I would be more concerned with destroying your sound card, than getting in trouble
with the phone company.  There can be a significant voltage spike on the phone line
during a lightning storm, and the ringing voltage can go up to 100 volts.  I suggest
that you use a small (inexpensive) isolation transformer, and a varistor on the sound
card side to squelch the transients.  This is the typical way devices like modems are
designed.  There are a number of good books on telephone line interfacing which will
define the on-hook and off-hook line conditioning.  I wish I could be of more help
but it has been 12 years since I did modem designs for a living.  Incidentally, the
FCC had a spec which required the attached equiptment to withstand 10,000 volt spikes
(of short duration).

Gary Gendel