That would depend on what type of KSU you're using and how it was configured at install.....not enough information to answer your question completely.

If you have the TVA picking up all calls immediately, you would need to edit keypad assignments in the applicable custom service menu....again, don't have enough information...if the operator's phone rings (to allow a person to answer) before the TVA picks up then this would not apply....setting would be within the KSU.