As a test a few days ago I disabled port forwarding to my PAP2 and have not had any issues. Setup is PAP2 ->Linksys WRT54GS (DD-WRT)->At&t 2-wire -> World

No problems with in or outgoing calls. Call quality is fine. Unless your running a freaking Cisco router you probably do not need to forward anything. More complex routers like a Cisco that control everything in/out of the router would be a different story.