I had a small S-class office, the handset displays would go crazy with small zeros & arrows & weird stuff happening, when I took it back to my office it worked perfectly.
The office where this was happening had a lot of electro magnetic noise, anyway I remember tech support sent a new ksu and I got it working.
Also in some under 10 seat offices some of the wiring can be a nightmare with loop out loop in things happening, you may think the ESI phone is the only thing connected to that circuit but actually there are other devices on the line.
