When the phone is idle, it normally displays the date, time. It may also shown you extension number and, in the bottom left, some of the following status letters.

B = Barred
A B is shown on your phone's display when the system administrator has set you to outgoing call barred status. You will only be able to make internal calls while this is applied.

D = Diverting (Forwarding) Calls
A D is shown on your phone's idle display when you have forward unconditional enabled.

G = Group Member (In Group)
A G is shown on your phone's idle display when have been configured as a member of a hunt group and your membership is enabled. While this is the case, you may receive calls targeted to the hunt group.

N = No Calls (Do Not Disturb)
An N is shown on your phone's idle display when you have do not disturb enabled.

T = Twinned
A T is shown on the phone's idle display if it is internally twinned with your phone. Calls to you will alert on both phones and can be answered by you at either phone.

S = System Alarm
If you are configured as a system phone, an S in the phone's display indicates a system alarm.