This article is from the ZTerm FAQ, by Les Jones firstname.lastname@example.org with numerous contributions by others.
This one is near and dear to my heart, as I used to have the 2400
bps Modem for the Deaf(TM). ZTerm offers three ways to turn the
modem speaker off (AT M0), or to turn the speaker down (AT L0) if
it's on. (All 0's are zeroes, as they always are in the Hayes
language. The only exception is The ATOn command, which is used to
return the modem to online mode. In that case, "O" is an "oh". The
n is a placeholder for an integer number.) M1 turns the speaker
back on. L1 turns the volume back up.
1. You can manually do the deed by typing AT M0 or AT L0 before you
make a connection. This method is best if you only want to silence
the modem for some sessions.
2. To automatically change the volume when dialing a particular
service, enter AT M0 or AT L0 in the "Pre-dial init" field in that
service's Connection dialog. This method is best if you want the
speaker on for some services and off for others.
3. To automatically control the volume for all services, select
Modem Preferences. Click in the "Initialize" field and use the
cursor keys to move to the far right. Move the cursor just to the
left of ^M and type M0 or L0. This method is best if you want the
speaker off for every service, every time.
Incidentally, these three techniques work for any initialization