i found these threads at the official PS3 forums:
Guide To Opening Ports On Your Router
and
Guide to making your PS3 into a DMZ
which both discuss unblocking incoming ports to the PS3 to bypass the following problems
* not being able to join rooms
* not being able to speak over headset
* not being able to hear over headset
* not being able to join games which are hosted by certain people
* not being able to join games that are no longer in the lobby, but are being played
There are obvious security issues to consider but i am unaware of any viruses currently written to target PS3's (*crosses fingers and prays that he hasn't unleashed an army of hackers into breaking everyones new toys*).
I hope this is of use to some of you
Posts
"BTW. just some more info on the NAT connection issues. When we first tried to connect, both Brand and myself were unable to establish a connection either in EOJ or in chat. We both have TYPE 3 NAT on our network connections.
The solution to our problem was discovered when I found out that my PC and my PS3 had both been assigned the same IP address by my router. By simply turning off my PC we were able to connect with absolutely no problems whatsoever.
My recommendation for anyone with NAT TYPE 3 who is having trouble connection is to simply turn off all other wireless devices. There seems to be an issue with the PS3 where it doesn't play nice with SOHO routers which results in conflicting IP address assignments.
If you have any questions or need help with connection issues, please feel free to PM me and I will see what I can do to help.
Thanks,
Whitewolfjm"
3DS Friend Name: Whitewolfjm
Pokemon Y In-game name: Superman