Voicemail FRAUD Question

[problemfixr]

I've got a NAM w/ 4.1 software. Routing is set up with a destination codes of "90" and "9011". This sends the calls to the Adtran 830 and it handles the "pointing" of the outbound call. The problem is when a call is answered by the auto attendant some has figured out that you can dial "90" or "9011", get stutter dialtone and then make an outbound call. I've temporarily disabled the lines ringing to the auto attendant. How can I block the NAM from either a) allowing an outbound transfer b) allowing the digits to be dialed or c) blocking long distance and international calls. Any information to help me resolve this situation is greatly appreciated.
Thanks in advance

 

[PERRYPJ]

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OLD ROLMEN WORKING ON NORTELS