Home automation: doorbell analog door phone intercom?

Answer doorbell with home phone:

I would like to create a setup in which a visitor rings the front doorbell that rings our home phones.  When we answer a phone it will act as an intercom so we can communicate with the people outside the front door.  There is no doorbell system in place so I am essentially starting from scratch.  I'd prefer doing this in an "analog" fashion since we are in a rural environment with unreliable power and no cell reception.  

Basically, I want to know if there's an easy/affordable DIY alternative to the several hundred dollar door phone systems I see available for sale. I would also like to install a remote electric door strike so I can lock/unlock the front door via our landline.

New phone shopping:
I need to buy a new home phone system anyway, since my mom only uses the speakerphone on the handsets and callers complain they can't hear her well.  Features I'd like:
--Power back-up operation (handsets work even in a power-outage)
--"Eco-Mode" where it consumes less power when you use it closer to the base
--Excellent speakerphone on handset
--Long battery life out of charger
--Lightweight, easy to hold/grip handsets with large easy to press buttons and clear display

There's several Panasonic models I've looked at that seem to fit the bill.  I'll admit I was initially tempted by the new Vtech video doorbell phone, but there's many characteristics about the actual phone/handsets that would make it difficult to use.

I wondered if getting a Bluetooth-enabled phone would be advantageous if a handsfree calling device could be connected, just like in the car but for the home phone.  But I don't know how to do that, if it's possible.

Just thought I'd mention the new phone shopping in case someone has any advice on best selections based on current home automation desires.