if you set the port in NT modes, which can connect with ISDN phone, but no incoming and outgoing line. if you want to make a outbound calls with ISDNｐｈｏｎｅ， ａｔ ｌｅａｓｔ one port should be TE and one port should be NT mode. the TE port connects with ISDN line. i think user manual has explained it. please read it. or you can go to asteriskguru.com and voip-info.org to find resource. it is sufficient for your case.