With your handset down, dial 355 then enter the extension of the phone you want to forward to. If you are forwarding outside of the building, dial 355, then your outgoing button, then the number you want to forward to. The display of your phone with say "FWD to xxxx"
To turn this off, dial 355, lift your handset and set it back down. Display of your phone will say "Any Call Forward Canceled"