I was looking around for pin out information with little success so I though posting some photos may help others.
As I did not want several connectors and coils of cable to connect my phone line to the Tel1 port on the HUB I purchased a standard RJ11 Lead (only needed 1/2 of it so did not matter what type.
You may need to substitute your colours with the cable positions of mine as many people will have different colour cables.
Existing Master (Ignore 2nd Line on Left)
The end of the 1/2 of the RJ11 Lead I am Using
Pin 1 Black
Pin 2 Red
Pin 3 Green
Pin 4 Yellow
Only Pin 2 and 3 are required.
BT Front Face Plate Removed
2 - Blue
5 - White / Blue
Notice numbers are 5 3 2
Fed cables through into the back
Connected :
Extension 2 - Blue - Red - RJ11 2
Extension 5 - White/Blue - Green RJ11 3
Regardless of cable colours as mine may well be different to yours :
Extension 2 - RJ11 2
Extension 5 - RJ11 3
Front replaced with connections inside
All Plugged in and working
So now I have my main phone working on its extension with a RJ11 'flying lead' from the back of the master socket to the Hub 3.
Plugging a phone into the master socket I get a dial tone for a temporary random phone number that BT has assigned (found with 17070), plugging into my extension (from the Hub 3) I get my number that was transferred to virgin media.