Both my aging mother and mother in law have cordless phones and often forget to press the OFF button when ending a phone call. This means that they can no longer be reached by phone, the calls immediately go to voice mail. In the past the fix was for me to drive across town to reset their phone. I've now figured out a great solution to the problem that allows their phones to be reset remotely either across town or across the country.
I don't know if this will work on all phones, but it does work on more than one version of Panasonic cordless phones. To test if it will work on your phone, end a phone call without pressing OFF, this will put the phone in the unreachable state. Then unplug the base station phone from power, and after a few seconds plug it back in again. If this resets all the phone to working order then this solution will work for you.
Knowing that the power reset fixes the problem, I realized there was a good solution. The solution is to plug the base station power into a smart plug. The smart plug that I had available was one from tp-link, while at my mother's house I used her wifi (yes, your parent will need to have a wifi connection) to configure the smart plug. I set up a dedicated account that I log into using the Kasa app from my phone, and from there it is very easy to turn the smart plug (and the phone plugged into it) off and then back on again. So now when I notice my mother's phone is unreachable, I log into the app and and reset her phone while sitting on my sofa at home. The Kasa app login can also be used by my sisters if they notice the problem before me.
The app could also be programmed to reset the phone every night when your mother is sleeping (if configured in this way the reset would happen regardless of the state of the phone) so that her phone will be available to callers in the morning.
I don't know if anyone else has this problem, but both my mother's have the problem so I think it's probably pretty common and the fix is so good that I wanted to share it.
Would still be much better to remember to press off or end.
I have an old cordless. The main base is a landline line phone. Cord and everything. The cordless has a charging base plugged into the wall. I pushed Talk, it made a dial noise (I think dialing into Comcast)hummed, then went into a busy signal and then nothing. I waited to see if the phone went off on its own, it didn't. But placing it into the charging base did. So if the Moms have a charging base, maybe they need to get into the habit of placing the phone there.
I wonder if the newer phones shut themselves off.
I got rid of that cordless and strung an extra long landline cord from the wall over to where he liked to sit, making sure he wouldn't trip over it. Never had a problem after that. Dad had landline phone in just about every room, anyway. And he knew how those worked.
My house also has landline phones in every room. No losing anything that big :)