I Am Having Problem in Transfering Calls on IP Phone Connected to VoIP Gateway to Other Phones on My Network?

We are having three SIP Accounts but are only having one IP Phone Device. We also have 4FXO i.e 4 Phone input Line and 4 LAN Port and 1 WAN Port VoIP Gateway.. What we want to do is that through that VoIP Gateway we would like to receive all the IP calls made to our IP Phone numbers to be received and or dialled from the same singal device. and also we need to transfer our call (if needed) to any other PC or Analog Phone on our network.