I'm not quite sure but why wouldn't you be able to plug the box into ethernet and then use the fxs ports for your sip trunks? I don't see "why" that wouldn't work. Perhaps a call to Adtran can confirm that?
Why would the fxs sip trunks care if they came via ethernet or T1/router port?
Problem there is you are paying for all of the other bells and whistles that you won't be using anyway.
Shrug...
Fred
