I had this idea for a few years now, to make an old land line phone with REAL BELLS work as a bluetooth headset for a cell phone. Now I can't take full credit for this as I heard of Steve Wozniac built one of these years ago. I loved the idea, and wanted to build my own.
Version 0.1 (previous version)
Simple handset from phone with bluetooth headset mounted inside. Very simple yet very eerie looking.
Version 0.2 has (Current Version)
1. Tabletop touch tone phone.
2. Dial tone.
3. Ability to dial out.
4. Working bells.
5. 10 cell NiMh battery pack.
Version 0.3 will feature (Researching/parts gathering)
All of Ver 0.2 plus following
1. Working rotary dial
2. 10 cell Sanyo Enelope battery pack.
3. Ext charger.
4. Auto/on switch.
Version 0.4 (planning)
All of Ver .3 plus
1. Internal charger.
2. flashing "ringer" light.
3. Ringer "silent" switch
4. Dial light via red LED
5. handset posts light via red LED
6. Internal Voltage regulating power supply, for continuous operation.
7. Universal External 12v/2a power supply.
Current model notes. Current 0.3 version trying to invent a way to mount the batteries. Best idea so far is to use 4-40 long bolts through the bottom and zip tie the packs to them, best semi- permanent mounting solution. Mounting the circuit boards are nearly the same way, using 4-40 screws with stand-offs. The Auto/on switch refers to the ability to have the device auto power off when charging plug is inserted into a "switched dc power jack". To get the rotary dial to work with the bluetooth board I have, I used a pulse-tone converter. The bluetooth board i'm using is the cobra Phonelinx. Which has been disassembled and soldered in power and phone lines. Later models I might desolder the board LEDs and mount them else where, but since I want this to mainly be obscure, I made it so you can only see them from underneath via small drill holes in the phone.
To make a "ringer flashing light" I thing i'm going to use a Radioshack neon bulb and mount, but use it only for the mount as it has the "look" that i want for a domed light. but since a neon would take more draw that needed and not be very bright. I will use a super bright red LED with a 100k resistor wired in parallel to the ringer.
The "Dial light" i'm still researching. An idea that came to me the other day was to use license plate bolts with LEDs already mounted in them, then to use a black rebar cover with a hole to cover the bolt, solving the mounting and the look as well as making it a fast solution. I cant mount LEDs from behind as there is to much mechanical gearing in the way from the dial. But using plastic fiber optic might be a future possibility.
The idea of using an internal charger is to be able to plug this unit in and have it work just like a desk phone and never have the battery die. Even though this adds complexity and cost, this really makes it a set it and forget it extension of your phone. This will also make it so you can use any dumb 12v cord that can supply 2a of current to run/charge the phone, i.e. in the car.
Work in progress as of 12-23-10