FreePBX 2.x includes a "General Settings Page." Among other things, the user can configure the "Operator Extension" for the "Company Directory." If you however over this option, there is no mention of the fact that this operator extension also applies to people who dial 0 while hearing a voicemail outgoing message.
I understand that the "Company Directory" is being phased out in Asterisk, and so I suspect that the "Company Directory" category is likely to be removed, which might inadvertently result in the removal of this option altogether.
For these reasons, I propose that "Operator Extension" be removed from the Company Directory area and moved to its own section. I also propose that the help bubble that pops up if you hover over the field be changed to indicate that it applies when users hit 0 while hearing an outgoing message from a voicemail.