Energis, which supplies the telecommunications network for Freeserve, is rumoured to be in talks with Centrica to provide phone calls to the gas company's 18 million customers.
BT spokesperson, Tony Henderson, said: "Telecommunications is a very competitive market and there are a lot of players. We believe our overall package of services gives us the edge. There is no such thing as a free lunch, and there's no such thing as a free phone-call. The customers will be paying somewhere along the line."