¤ Does your internet provider block ports? Some do, some don't. It's atleast worth looking into. I worked for a company that automatically blocked ports, a simple call to us and we would unblock them for customer.
Some routers/modems just won't do it. For years I couldn't get a decent NAT setting no matter what DMZ or forwarded ports I tried. I then got a new Router/Modem from my ISP and finally I could put my PS3 into the DMZ and get and Open NAT. Mind you thou I still have occasional problems on the PSN end if something updated my NAT goes from Open to Strict but simple power cycling my router/modem resets it to Open again.
Never got and open NAT with DLink, Linksys, or Zyxel no matter what setting used.
Achieved with Actiontec Q1000
I have a Juniper SSG-5 with all ports forwarding from both Untrust -> DMZ, and also DMZ -> Untrust. Untrust -> DMZ is natting fine and passes all other traffic defined in policies. Still, PS3 in DMZ zone can't host a team. I could specifically allow ports to be forwarded, but that doesn't make any sense because they're all open anyway (for testing purposes). Whether or not UPnP is enabled, as I understand it, all open ports *should* allow any traffic PS3 tries to create, what am I missing?