I guess all I'm looking for is some hint to give to the ISP. "IT doesn't work" doesnt help them any more than it helps you... and if they have no idea where to look for a problem that could be almost anywhere, they aren't likely to try hard at all.
On the other hand, the 2nd and third tier tech guys seemed capable, interested, and motivated to try to help. (Kinda refreshing for a corporate tech support system!) One guy got the link to sign up for a 2 week and try to reproduce the problem at home!
So what can I tell them to look for? That's what I need to take it to the next level. What are the ports for Orange, and the time frame for TA at 4000?
AND: How is received vox different from sent vox? (That seems to me to be the most important question of all -- if sent vox gets through, and received does not, then the problem is most likely to be solved looking at what's different between them, right?)