SysAcc-00 Ring - this is basically you intercom line to the operator. the 'ring' means it will ring other station when calling them, instead of voice-annoucing.
these next 3 are co lines for the system. as to whether or not they can be deleted, that depends on whether or not they get answered anywhere else.
Line 501 -I
Line 502 -I
Line 503 -I
thanks, tim