VoIP Phones - BT HomeHub
A BT HomeHub has a built in VoIP Client that works as a DECT base station. This has been known to work with the AA VoIP Service.
With upnp enabled, outbound calls worked, but not inbound. With upnp enabled, incoming failed and the log said:
FIREWALL icmp check (1 of 2): Protocol: ICMP Src ip: 188.8.131.52 Dst ip: 192.168.1.254 Type: Destination Unreachable Code: Port Unreacheable
This was a setup, where the HomeHub was inside the network being NATed by another ADSL router. In this case, the HomeHub was only acting as a wifi access point and phone.