Also, 4ESS (sometimes refered to as 'custom' by At+t) has a bunch of goofy settings to play with. If there is any chance to get them to change to National2, do it.......you will not need the bottle of Exedrin. Here in the Chicago suburbs, Joliet C.O. has a Siemens switch. Every time they've upgraded, the p-phones and ISDN sets have gone right in the toilet...............