Hi! I hope someone may be able to help! I'm not a technical expert in this field, but have responsibility for some aspects of IT at work, so am learning fast!

I recently acquired for work a 2925ac router to load balance 2 BT broadband connections. Only 1 broadband connection currently active. Next being installed soon.

Using the BT Business Hub 5 for the ADSL modem & have disabled DHCP & WiFi options. Set it's IP address manually & set the 2925ac router WAN1 IP address to something in the same range. Set the 2925ac LAN side IP address to be the same as the previous BT Hub IP & switched on the 2925ac DHCP and WiFi options. Renamed the SSID to the old BT SSID & set password accordingly and everything worked well. Internet access for all office PC's and uninterrupted WiFi access to all WiFi devices. So far so good.

We have a BT Quantum phone system with office based analogue, digital & IP phones. Also have IP phones with teleworker licence for use away from the office. They need to link back to the BT Quantum phone system. Previously the port forwarding was set-up on the BT Hub. Office based phones are working OK. The teleworker phones do not as it appears they can not connect back to the BT Quantum system.

Do I need to forward the ports on the BT hub to the 2925ac and then forward to the BT Quantum? How do I do that?

Or can ignore the forwarding on the BT Hub and just let all traffic through and forward from the 2925ac to the BT Quantum?

You should set the port forwarding in the 2925, and ideally set the BT HH into modem mode, otherwise you may well end up double-NATing which isn't a good place to be.

If you can't set the HH into modem mode, you may want to consider some HG612 (cheap off ebay) or Vigor 130s to use as your modems. Both will work equally well, but the HG612s off ebay will be significantly cheaper!