Hopefully someone will be able to help me on here with regards to an issue I'm having with some select outgoing calls. I've got the Cable Modem connected to an Apple Airport Extreme, and plugged into that is my VOIPo unit. Everything seems to work ok with the exception of placing calls to a few numbers, when I just get 'dead air' and then a fast busy signal. The receiving party state their phone rings and when they pick up, sometimes they hear me, sometimes they get 'dead air'. I can never hear them, all I get is a fast busy signal after about 30seconds.
I've called Tech Support several times with no luck, they've even remotely accessed my computer to try and alter the Airport settings, with no joy. I've read several forums where they talk about altering the NAT settings or some sort of Port conflict. Anybody have any clue how I can go about fixing this issue? I'm not too familiar with altering these settings, so any help would be appreciated.
I know the problem now lies with the Airport, as I have isolated that and simply plugged the VOIPo unit directly into the back of the Cable modem without any calling problems.
The problem is getting old real quick! What started out with a few select numbers, seems to be growing by the day, with the same issue happening on too many calls now!

Thanks for any help any of you can provide!