AT&T MERLIN LEGEND Release 3.1 System Manager's Manual page 180

Applications
Monitor SMDR reports or Call Accounting System reports for outgoing
calls that might be originated by voice messaging ports.
A 012 or 016 port (Release 4.0 and later) that is programmed as a generic
VMI port can transfer an outside call to an outside number. A single-line
telephone, connected to an integrated VMI port can complete trunk-to-
trunk transfers. In Release 3.1 and later systems, trunk-to-trunk transfer is
automatically disallowed for all extensions, unless it has been enabled (on
a per-extension basis) through system programming.
Calling restrictions (for example, Disallowed Lists, Toll Restriction, Facility
Restriction Levels) should be programmed, as appropriate, to minimize
toll fraud abuse, especially if a single-line telephone is connected to an
integrated VMI port. Refer to the "Calling Restrictions" section in the
Feature Reference for additional information about programming calling
restrictions.
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Features and Applications
Assign toll restriction levels to all voice messaging ports. In Release
3.1 and later systems, voice messaging ports are automatically
outward-restricted, assigned an FRL of 0 (Hybrid/PBX mode only),
and assigned a Disallowed List that restricts calls to many numbers
often dialed by toll-fraud abusers.
If you do not need to use the outcalling feature, completely restrict
the outward calling capability of the voice messaging ports (this is
the default in Release 3.1 and later systems). For AUDIX Voice
Power and MERLIN MAIL, use the "transfer to subscribers only"
feature to restrict outside calls.