PABX system, 4 CO line,16 Extension

Concurrent Call: 7
DISA
Caller ID(CLI)
Operator setting
Auto attendant(OGM)
Intercom call
Call transfer
Call forward
Call pickup
Call duration limit
C.O line booking
C.O line on hold
Day & night mode(manual)
Three party conference
Outgoing call level setting
Speed dialing(memory dialing)
Multiple work mode (manual/auto attendant/CRBT) 
Multiple dialing out mode (direct/indirect/choose CO line) 
Ext. Number flexible coding (change extension number freely 
Busy tone detection