I have a 12 button digital wall phone that goes off hook randomnly. The wall clip is oriented correctly. The phone is set to automatic outgoing line. As such it picks line 1, then gets re-order tone from the telco. The customer will hang up and then it will re-occur. I have replaced the phone and it still happens. My next step would be to replace the jack, move the station to another port and change the pair. Could it be anything else like a bad card?

Possibly has auto answer activated or camp on from a trunk?

A new jack, cable pair and a different extension and different phone all put in place to see what happens.