I have a 2811 with the Advanced IP Services IOS loaded. I have two T1 lines for data and a T1 PRI for voice, as well as an external Linksys router with another internet connection all routing through the router. All connections and the CME work properly, but once I enable the IOS firewall, the voicemail stops working (complete silence when you attempt to access it). If I disable the firewall the voicemail comes back on-line. I plan on disabling the external internet connection once the T1 lines are secure, but I can't afford to go without the voicemail in my organization. Is there a series of ports or a specific service I can allow through the firewall to allow the voicemail to work? I haven't been able to locate any documentation that would answer this for me.