Everything works but audio (?!?!?!?!)

So I set up the last STABLE version of Trixbox that includes Asterisk 1.2.23, installed it according to what little comprehensive documentation I could find on the internet, and after a great deal of tweaking (with routers and ports and such), got things to the point where I can make and receive calls to regular phone numbers.

Only problem is there’s no audio. None whatsoever, beyond the ring sound.

So I don’t waste everyone’s time posting the wrong stuff, where should I start? I’ll tell you in advance that I’m using Zoiper on a Windows Vista laptop, with a Bluetooth headset that works perfectly for everything else (and the audio meters in Zoiper show that I’m sending audio, although that audio never gets to the other end of the phone…)

I’m testing the line by calling my Vonage soft phone number from my home number (which is a hard-wired Vonage number). Asterisk box has a static IP address, laptop is behind a firewall with ports 5060-5068 opened for SIP, and ports 10001-12000 opened for RTP (same ones I have configured in rtp.conf).

I’ve spent three days trying to troubleshoot this, have searched for every combination of terms on something like forty different sites, no answers yet. Lots of people with similar problems who say “fixed it”, but never say how.

I’d be grateful for the help so I can get back to running my foundation and stop playing Alexander Graham Bell.