I'm having this same issue. While the users report hearing a short tone on the handset (similar to call-waiting), they don't know that is signalling another incoming call. I see this on both 7940 and 7960 phones. The incoming lines do show the animated icon on the phone, but aside from the short beep on the handset, the user does not have any indication that another line is ringing, and many calls are going to the Auto Attendant.
Could this issue be the firmware for the phone?
Any info would be great!
Thanks,
Roger