Tim and company:
Ok relative to my post above, I took my pots line off hook and just let the dial tone drone on without dialing.

I picked up my 212 372 XXXX voipo line and called the pots line 631 361 XXXX and got the goodbye greeting.

I then dialed my cell from my pots, thereby establishing a supervised open call. I picked up my voipo line 212 372 XXXX and called the pots 631 361 XXXX and got ringback tone from voipo and got a call waiting tone on my pots line.

I repeated this test twice with the same results.
Look in my call logs for Friday evening around 11:55 PM

1st call failed
2nd worked
3rd failed
4th worked.

Its the damn header/traveling servicemark that is confusing the voipo equipment when the line is in a dialing state as opposed to a connected or "engaged" call.

When we used to encounter this stuff at Verizon, we simply charged more for it......

Hope that helps.