"NAT pinhole" is the term?
My last three consumer routers didn't need port-forwarding. Nor this semi-pro one (Cradlepoint MBR900 - great, by the way).

So is it some of the D-Link and Netgear crap out there?

Sure is a mess 'o packets flying out.
Do all the VoIP providers have to do this? I don't recall seeing it with two others.