last year i moved house. my phone was discinnected 3 weeks before moving but i still had my broadband. so, do i need to keep my bt phone in order to have my broadband?
although your phone line was unable to make chargeable calls out wards it will still have been able to receive calls and make 0800 calls (free)
but after a set time BT will stop all use of the line (they used to years ago, are not sure about now), then they could charge the new user £100 + to reconnect the line.