We had a client who had Panasonic digital KSU's in three of his homes, he built a hanger and was talked into replacing them all with a Cisco VOIP system by the T-1 guy. Needless to say he ripped them all out after two days, you couldn't even intercom in one touch like the Panasonics because the "endpoints" didn't have one touch assignable buttons, you literally had to scroll through a list just like on your cell phone to intercom or call another room, as well as with any other function such as transferrinng calls and so on. Beware of functionality!!