Would you believe this is a mobile phone?
SparkFun’s newly redesigned portable rotary phone ($249.95 USD) has been upgraded to work with any Bluetooth phone. Just pair the “portable” phone with your cell phone, and you can send and receive calls on this old school rotary phone. Even the ringer, analog dial and dial tone work the way you’d expect them to. And since the phone runs on a powerful rechargeable Lithium-Polymer battery, you really can take it anywhere.
Now I just need a portable version of my Batphone, and I’ll be all set.