PAP2T-NA intra-line conflict

Line 1: Voipo - used basic settings in http://forums.voipo.com/showthread.php?t=1182 and http://support.voipo.com/screenshots/pap2t/ (not provisioning) and tweaked to work with my NAT, enable faxing...
Line 2: Gizmo5 - used settings on Gizmo forum

Been messing around with SIP softphones and IP phones for years. Recently got an unlocked PAP2T-NA so I could use Gizmo5 and what ended up being Voipo with POTS phones.

Each line individually seems to work fine, but not when both are registered. I figure Google Voice simulringing 619-393-2253 to Gizmo5 and Voipo 949-xxx-xxx could be a problem, and/or AT&T landline (porting in progress) forwarding to 619-393-2253 and then simulringing G5 and 949-xxx-xxxx, and/or people calling from bloody AT&T iPhones another, but maybe it isn't so obvious...

1) iPhone cellphone call to AT&T landline>Google Voice simulring numbers. Picked up on Voipo line. Talked for ~5 minutes with dropouts galore. Around 6th minute, Gizmo5 line started ringing. Picked up, was conferenced in to the Voipo line without DTMFing anything - call logs show no other number was calling, the only one was the iPhone. WTF? Did it hear a false DTMF in the voices?
2) Can't seem to answer either line during random rings without getting dead air. Sometimes 1, sometimes 2, sometimes 3, etc... pick up, dead air, hang up, phone rings immediately.
3) Another iPhone cellphone call, I suspect (assuming the caller had the same phone as when I last saw them using it), dropouts galore

The behavior is so inconsistent; I hate giving and receiving tech support like this...

I hope the port gets done well in advance of the 30-day trial so I can kill the Google Voice bouncing and see if there's any improvement.

Let me know if I should print PDF screenshots, redact, and attach here.