3Com NBX 100 Administrator's Manual page 243

Account Codes 243
Conference
During the time that forced account code mode is enabled, an account
code must be entered for each leg of a conference. The account code
applies to the call leg, and not to the call from which the conference is
initiated. After the conference is completed, an account code entered by
any user overrides the account code for the conference call.
Emergency Numbers
Emergency numbers are allowed without entering an account code.
Call Forwarding
Account codes cannot be specified as part of a forwarding number. If a
call is forwarded while forced account code entry is enabled, the call is
forwarded and the user is not prompted to enter an account code. A side
effect of this feature interaction is that an internal extension could be
used to forward calls to an external number and thereby circumvent
forced account code entry.
International Dialing
If a timeout occurs while dialing after you have entered the minimum
number of digits, and Force mode is enabled, you are prompted to enter
an account code. After you enter the account code, you can continue
entering digits for the international number.
Paging
You can use Paging without entering an account code.
Call Park
If you entered an account code before parking a call, that call is preserved
when unparked. You can unpark calls without entering an account code.
You can enter a new account code after unparking the call.
Redial
Account codes are not stored as part of the redial digits (except on analog
phones), even if the account code was specified as part of a speed dial
operation. If outbound digits are redialed while forced account code
mode is enabled, the user is prompted to enter an account code.