Some clarification on my earlier post.
I always opt for the simpler solutions wherever I can, and I fully endorse CTylor's comments regarding letting STUN do the router sorting out.
My suggestion was primarily to address the problems I experienced when the same Voxalot account was logged onto by 2 or more ATAs/SIP phones operating behind the same public IP address.
For all I know, the problems may have been due to the particular router and SIP devices being used.
For a
single ATA, I have generally found that using just DHCP & STUN is sufficient, without the need of any port forwarding.
For
multiple devices logging onto
different SIP services (Eg. Voxalot and FWD), STUN is also usually sufficient.
For whatever it is worth, Wikipedia states that "STUN will not work with Symmetric NAT".
Simple traversal of UDP over NATs - Wikipedia, the free encyclopedia
A word of caution regarding uPnP - Earlier this year, there were reports about a security flaw when using uPnP, and I have not found any indication that this is resolved.
Severe UPnP Flaw Allows Router Hijacking -- Computer Security -- InformationWeek
Flash UPnP Attack FAQ | GNUCITIZEN