ok, finally got the 3970 fully working
key things :
Make sure you're on the latest firmware (allows VLAN changes)
Choose VLAN 101
ATM must be set manual
usename : [email protected]
For voice interference problems, i did the following :
Tried my 3970 on a friends infinity. All worked perfectly - no interference ...
So I researched and found that the BT wiring coming into my house (one pair - BLUE/white and WHITE/BLUE). In my case it appeared that they had been wired incorrectly to the A and B termination points - so, er, naturally I called up BT and asked them to swap them round for me, cos you're not allowed to swap them by yourself ...
After that was done, everything works perfectly !!!
Hope it helps !