To forward extension on Trixbox Asterisk server:

• Login to admin web GUI
• PBX > PBX Settings > Extension > [extension]
• Under Device Options change value of field dial
• To forward to an extension on the same VOIP server:
  SIP/601
  Where: 601 – extension you are forwarding to
• To forward to an extension to another outgoing trunk:
  IAX2/Boston/601
  Where: IAX2/Boston – trunk name; 601 – extension you are forwarding to

Trixbox v2.6.2.2