bluetooth to rj11 converter?

Why doesn’t this exist?

I have a mobile phone as my only phone, but it doesn’t get very good reception in my apartment. I am planning to get a bluetooth handsfree device so I can put the phone in the window where it gets good reception and carry the handsfree anywhere in the apartment and still get a signal.

That got me thinking. Why not create a device that has bluetooth and an rj11 connector on it? You set up the converter so whenever it sees the mobile phone in range it becomes a “handsfree device” connected to it. It then converts all of the handsfree functions — dialling, ringing, caller id, voice — to regular telephone spec. It could even fake a dial tone when it sees the mobile, and play silence when it’s not found. You then connect any cheap-ass phone to the rj11 and you instantly have a “home phone.”

I’ve done some searching on google, and the only devices I can find are converters to go from an existing landline to a bluetooth headset. What ever happened to marketing to us hip singles who don’t want a landline? This seems like such an obvious use-case.

Anyway, if there’s anyone out there who knows electrical engineering or has access to a bluetooth chip, let me know. We could create a new product and get bought by jabra or something!