using below phone
Phone Information
Phone Model VVX 500
Part Number 3111-44500-001 Rev:A
MAC Address 64:16:7F:96:FC:D7
IP ModeIPv4
IP Address 172.16.16.249
UC Software Version 5.9.1.0615
Updater Version 5.9.7.12459
Camera Software Version 1.0.0
my phone shows setting->basic->ring type->
1 Default
2 Line 1 (3111)
3 Attendant Calls .
i want to know when 'Attendant Calls' option appears ?, i'm unable to find it out .