I have a BT Sonus phone and last week we received a cold call and there was no one there. When we hung up our end the phone said on the display "line in use". BT checked the line and I have since plugged another phone into the line and this one works fine but if I plug the Sonus back in it still says "line in use".

Any ideas how I can convince my phone that it isn't in use?

Thanks for your help

Have you power cycled the phone? (you may need to remove batteries in both the base and handset)

Yeah - tried that