I have the above mentioned ATA. The instruction manual that came with it (a33 page PDF on disk) is nearly worthless. It doesn't even mention most of the features and configuration options on the set-up utility. There are setting for two lines and two users. I have no idea how you specify a user. I don't understand how to use the calling features like call waiting. I don't know what some of the call forwarding settings mean, like "block last caller" and "accept last caller." Under "supplementary Service Setting" I don't know what "Block ANC Setting - Yes/No" means nor do I know what "Secure Call Setting - Yes/No" means.
I know this is probably really transparent to most people, but I'm just not much of a phone junky and some of the set-up just isn't clear to me.