Background. The Grandstream HT has one FXO and one FXS port. Setting them up an FXO port in FreePBX/ Asterisk has many steps and it. Grandstream HT is an ATA with one FXO port and one FXS port. The HT from Grandstream also features a built-in router and two Ethernet ports. : GrandStream HT 1-FXS/1-FXO Port Analog Telephone: Voip Telephone Grandstream Powerful 2-Port ATA with Gigabit NAT Router.