Chevy, what ISP is involved? Is this one of the cable providers? Comcast, TWC, Charter, Cox, etc?

I'm getting sporadic reports of busy on outbound as well, mostly from customers using one of those cable services.

Most of it seems to go away when I move them to SIP7.

I suspect voipo can't duplicate it, because they are not able to test via Comcast, Time Warner, etc. But I can't confirm that.