I have a pair also.
In the various VoIP services since late 2003, I've never port forwarded.
I do admit there were times where they were direct connect to the modem with the help of a switch.

Currently both are behind Tomato 1.23
Not because I asked, but one has ports 5061 and 5062.
The other has ports 5061 and 5062.
(Before the PAP2T software update, they were different.)