(OK so it's not really a computer question but it will require a geeky type answer)

The problem:
My Parents are getting older, and although they have had and used cutting edge technology longer than most people here, some things change with age. Dad changed over from the local telco to voice over cable with Comcast (the Triple Play - TV, Internet and Voice). Ever since they have had a growing problem with their home telephones. The Panasonic expandable set I got them 2 years ago suddenly "wasn't as reliable" as it always had been. Calls would be dropped or receive interference at times. Mom wanted them replaced. So while I was home in the Fall I brought those back to Costco and got a different expandable set of Panasonics only this time got the DECT units. It worked absolutely fine while I was there. After I'm back in VA I start hearing that the phone stays busy for hours at a time. It seems that both of them are forgetting to push the END Call button when done with a call. Now with telco service after a few minutes of the line being left open you get a recording and then that extra loud nasty alarm sound that alerts you to the phone that was left off hook. Apparently cable phone service does not have this feature and if the phone is left off hook it just stays open until the handset is turned off.

The Question:

Short of returning them to wired handset phones which would require me going to Chicago and rewiring several rooms that either never had phone jacks in them or the jacks were cut off when the cable guy installed the cable phone unit. (He claimed that there should only be 1 jack active coming from the cable modem/phone unit and cut and/or removed wires from distribution jacks so that the other jacks in the house are not actively connected any longer) Is there a device that would add a warning tone if the line is left open with no activity for a certain amount of time, or is there a type or model of cordless phone that does not require hitting an "End" button after any call?

They have had cordless handsets for the last 3 decades and are able to use their cell phones without forgetting to hit "End", so the whole thing baffles me. But the point now is to find a solution that will work for them.

How about a sticker on the handset saying "PRESS END" or whatever button needs to be pressed to turn off the phone.

With our cordless phones they'll hang up when placed in the cradle. I'd imagine the ones your folks have would do the same, so maybe intruct them to put the phone back in the cradle when done with a call.

I think I remember there is a way to rewire the phone jacks in a house to support VOIP - if you have the time and they are not going back to POTS, that would also solve the problem.

not so much as rewiring as just plugging the VOIP connection directly into the phone line should work as long as the telco end is already disconnected.