3Com Courier Reference page 90

11-10 C 11: D
HAPTER IAL SECURITY
WARNING: If you do not use the ATZ command to end a remote-access
session, Dial Security will remain disabled at the host, and anyone dialing
in to the host for remote access will have access to the ATI10 screen and
all Dial Security accounts.
DTMF Security
DTMF (Dual Tone Multi-Frequency) Security requires a modem to go off
hook when it receives a call but keep silent until it receives the valid DTMF
password. After the modem receives the valid password, it will begin
training. If the DTMF password is invalid, the modem will go on hook,
and the DTE will never know there had been a call coming.
The DTMF security status and password are shown in the ati10 screen
DTMF security is enabled by setting the S53 bit 3, e.g. S53=8 or S53.3=1.
Using the %D command sets the DTMF security password (AT%D=PWn,
n=0--39). Make sure to disable that account so no one can use the DTMF
password as the Dial Security account. For example, to set local modem
DTMF security password, you may use following command:
AT%A0=123456,N,,, then AT%D=PW0. You can change that security
account later, if you like.
The DTMF password can be the combination of 0123456789*ABCD; the
# is used as the password end sign. The maximum length of the DTMF
password is 8 character.
The remote modem dial string should look like this
ATDT2625000@123456#. In this example, "123456" is the DTMF
security password.