What type of phone are you using,7310,7316,7208 etc
Chect the Button (Feature *0)
if you want an extn to be seen on a button(internal autodial)
press feature *2
press the button you want it to appear on.
enter the extn number.
as long as the button has a LED then you should see it.
if its a Physical line appearance you what to see then it has to be the same line number on all phone.
eg line 061 to appear on all phones.
If you are using a TARGET line programmed to appear on all phones eg,125 then the 1st call that answers it the LED will light UP but the rest of the phones LED will be OUT .