Iwatsu ENTERPROSE-CS Owner's Manual page 227

(Polycom):
While on an outside call:
 Press the transfer soft key.
 Dial the extension.
 When you hear busy ring back tone.
 Press the transfer soft key.
To answer a Camp-On call:
Analog SLT only. Not supported on SIP phones.
 Hang up on the first call.
 Answer the second call, or
 Place the first call on Hold or Call Park.
 Hang up or press the receiver button.
 Answer the second call.
Clear Call
Analog SLT only. Not supported on SIP phones.
When you make an intercom call, but the called extension cannot be reached,
and you wish to call another extension:
 Do no hang up.
 Dial the second extension number.
Conference
Add-On
(up to 1 outside & 3 inside parties or 4 inside parties)
While speaking on an outside or intercom call:
 Press and release the receiver button quickly or press the Flash key.
 Dial the extension number of the party you wish to add.
 When the party answers, press and release the receiver button quickly or
press the Flash key.
After you hear a tone, all parties will be connected.
To add another extension, repeat the same procedure.
Polycom SIP station – Not supported.
SIP & SINGLE LINE TELEPHONE USER GUIDE - 209