Its not a wiring issue because video and files download fast and smoothly.
It may be a noise issue but ping tests show quite a smooth connection.
I've asked the client to try out their old Orange provided Netgear router and see if its any better.
Thanks for your reply.
Hi, There is reference to Internet telephony on the EE Bright Box router Port Triggers page under NAT > Port Triggers�
Port Triggers
Some applications require multiple connections, such as Internet gaming, video conferencing, Internet telephony and others. These applications don't always work when Network Address Translation (NAT) is enabled. If you need to run applications that require multiple connections, specify the port normally associated with an application in the "Trigger Port" field, select the protocol type as TCP or UDP, then enter the public ports associated with the trigger port to open them for inbound traffic.
Note: The range of the Trigger Ports is from 1 to 65535.