Why is my phone flasing all the time and it shows extension in use, and I can't make a call?

Question

Why is my phone flasing all the time and it shows extension in use, and I can't make a call?

Answer 1

Try unplugging all the phones from all the jacks and just fix oen phone in the demarcation jack and see if you have a dial tone , if you dont have contact your service provider

if you have a dial tone on the demaraction point

see if you have a fax machine or anyother machine is connected to the same line and if it is use

or see if there is any problem with your hand set.