NORSTAR Voip Gateway for Remote Phone

Hi everybody, I read the Norstar voip gateway, I noticed it is for site to site, in my case I got a Norstar Mics on the head office with an existing users and I want to give the other users located on the other site the possibility to call users located in the head office, like real communication over the internet using a voip gateway such as Norstar voip gateway. But as I said it only mentioned for Norstar to Norstar,. Could it be possible for Norstar to extension using the "Norstar voip gateway device" for a distance location? Any idea will help me. .. thanks,