[Asterisk-Users] AASTRA 9133i and PIX Firewall

[Matt]

Hi,
Does anyone have experience with the Aastra 9133i and a PIX firewall? 
My problem is that it passes data with no problem at all (that being
audio goes fine)... however my voicemail notifications do not work. 
If I take the phone OUT from behind the PIX firewall, voicemail
notifications work.   What do I need to do (on phone, firewall, or
asterisk) to get the msgwaiting indicator to work?