Actually, we see this a on occasion... The easiest fix is to take a small paper clip and make a small right angle bend at the end, only a couple millimeters long, then remove the handset cord from the handset, put the right angle piece of the paperclip behind the tension finger contacts in the handset and lift them a bit to increase the tension they put on the handset cord contacts. Not a 100% fix, but works most of the time for a significant amount of time.