What do you mean that it is not working? You need to provide some specifics here. Is the A800 configured at all or did you simply plug the GSM in to the A800, with no config, and expect it to work? Did you check the alarms on the A800 to see if the unit is in bypass mode? Have you tried using the test command (test o x where x is the pstn line number to test for dial tone, then test e to end the test).
Or is it a routing problem. The more information you provide, the better assistance we can provide.