The people at Medium have a very interesting collection called ‘Products I wish existed‘
There you can find some interesting ideas for your next endeavor 🙂
My product I wish existed? A device that would allow me to use my mobile phone on the fixed phone line.

Here’s why.
They did not evolve too much since the rotary phone. For over a decade we have cordless (DECT) phones, but even the ones produced this years have modest quality (to say the least) and are not that cheap.
Their rechargeable battery has a very short life because of the frequent on the charger/off the charger cycle. Their display is miserable. And if you wish features like voice message, missed call notification or ‘do not disturb’ schedule, you will have to pay the price of a smartphone.
The fixed phones are slowly dying.

I would replace them with the following solution:
-a base where the landline would connect
PLUS
-wi-fi/bluetooth
PLUS
-your favorite smartphone via an application.

Think about it!

When you’re not at home, the base would record your messages. When you arrive home and enter your home network, the base pushes the messages on your smartphone.
Then, in order to make a phone call on the landline, you open a dedicated app, and simply use your smartphone as a DECT phone.
The same app on your smartphone would be able to take an incoming call when you’re in the home network.

The base producer would have to take half of the DECT technology (the base), eliminate the crappy DECT phone, put some wi-fi/bluetooth chip inside it and make an app that would be freely distributed.

I wish this product existed 🙂

Later edit: There is other products like I800 iCreations ($249) or Panasonic’s link to Cell line. But they do the opposite: taking the smartphone calls to the DECT phone: “Link your cell phone to your home phone”. I want to get rid of my home phone and use my smartphone instead 🙂
This guy is apparently on the good track, but it only looks like a hobby, not a commercial product.