Sounds like something you should talk to ATT tech support about.  AT&T does
their own digital phone service and could be routing calls through that.  You
never can be sure why AT&T does things the way they do, but it usually involves
money.

-- 
Chad Walstrom <chewie at wookimus.net>                 | a.k.a. ^chewie
http://www.wookimus.net/                            | s.k.a. gunnarr