Have a BT Freestyle 750, works fine for making and receiving calls.
If an incoming call or outgoing call is made whilst using SKY ADSL Hub wifi network, the network disconnects from the hub and the internet connection is lost !
If the Freestyle 750 phones are disconnected from the phone sockets then the problem doesn't exist and other phones in the house work fine without causing any problems with the ADSL connection.
In fact, if all phone sockets are cleared and nothing is connected to the telephone sytem apart from the modem/router and there is a live connection to the internet, simply by plugging in one of the Freestyle 750 (master or slave) phones the wireless network connection is imeadiately dropped. Given time the network re-connects.
All telephone sockets have been replaced ( 1 master + 3 extension sockets) and a new router/modem has been installed and the problem still exists.