A further thought: If your VIRGIN internet modem/router has built in DECT*, then you may be able to connect Beocom 6000s straight to it cordlessly without using the B&O PSTN. I have used Beocom 6000s like this in the past (with a German router) – there will be reduced functionality but calls in/out should work fine.
* I just opened a webchat with Virgin to see if any of their hubs had built in DECT – unfortunately I very much doubt that the virgin ‘assistant’ understood my question! I would take his answer with a pinch of salt, but he did say: ‘Our Hub 3 and Hub 4 has a built in DECT, alright?’
Personally I would have a look in the router’s menu and see if there are any landline/DECT connection options.
