We have a 2 line phone. One of the lines shows 'in use" and it is not being used. When you call it, the message says to enter your mail box code.

It sounds like the one handset has not released the line. What you want to do is take the battery out of the headset and unplug the base station for about 30 seconds. Then plug the base back in. That shoudl force the line to reset. Next plug the battery back into the headset. Try it and see if it functions normally or it locks the line again. I'm hoping this is just a one time glitch and not a failure. If the line works normally then hopefully this is a one time event. If it locks the line again then the handset needs to be replaced. It's also possible this is a indication of things to come. If it works after resetting the two, it might ocur again. If you can clear it and it keeps repeating, it may do so more and more until it no longer resets the line. There is a slight possability this is a base station error but thats pretty uncommon. Unfortunetly there is little you can do to repair the handset and it would definitly not be worth doing so. Basically your only option is replacment.