Apologies for the lack of info about the Alcatel, it's not a system that I've touched before, and not one that I technically have access to to troubleshot in this instance.
I believe it is an OXO, but will check that tomorrow. There are two limiting problems aside from not knowing the Alcatel. The first is the distance, it is from australia to Vietnam. The second is the language barrier and the experience of the tech over there!
I can get access to the system if required, but having never seen it before makes it harder, but I will check out your suggestions. From what I could see though yes the sip config options are very simple and limited.