The person that told you this is wrong. These kits are for extending the "internet" connection. They pass the ethernet over the mains cabling. The sockets on the bottom of the wifi (2nd device) are the ethernet ports.  Landlines are analogue 2 wire. The extend the landline you need a cable. There used to be plugged in extenders for landline phones but they are very uncommon now

zzfirpo wrote

Hello, this question might sound stupid but I have literally zero knowledge in these things so...

We have a landline phone which is plugged into the only working phone outlet with an RJ11 cable. We can't rewire the house but we need a second phone on the ground floor and for reasons I can't really explain here it can't be a wireless/cordless phone so we were told by an electrician we should buy this kit and just plug the second phone and that's it. It sounds fair because there's just one cable that brings both the Internet connection and the phone line to our house. My question is, this has ethernet ports, so can we use it for a telephone line? If we can, we just plug in the RJ11 cable of the device or do we need an ethernet-RJ11 adapter? Then we just plug a cable from the existing phone outlet to the first ethernet of this device and plug our existing phone to the second ethernet and the second (new) phone to the second device of the kit and that's how it would get the phone signal? Also, do the two sockets need to be wired to the same circuit breaker?

Again, this was an electrician's idea, I have no clue whether it might even work in the first place so... any help is much appreciated.

Thank you very much for both of you. I knew something wasn't quite right about this...

Thank you again, best regards