FXS / VoIP Hybrid Line

We’re about to launch a small business and are looking to set up two new lines for the business, but we already have a Nortel PBX with 6 lines in place. My employer is looking to have a VoIP line AND a POTS line connecting to the same phone (he’s concerned about the consistency and reliability of a VoIP line and wants the POTS system in place in case of failures on the VoIP side). Does anyone know how this could be accomplished? We’re considering both building a system and purchasing a turnkey solution, so all ideas are welcomed.

  1. Install Asterisk with an FXO interface (see the Digium website) and Internet connection
  2. Configure DAHDI for the FXO interface and sip for the VOIP lines.
  3. Connect internal phones either by the local network (sip) or FXS interfaces on the Asterisk box.
  4. Write a dialplan so you can choose which line you want to use.