This is pretty awesome, however, a little impractical. So, you can use bluetooth with it to receive phone calls - why not just have a regular phone in your pocket? Texting will be annoying to use. All of the other features phones have such as camera, internet, etc, won't be present. Once again, music streaming can also be done via bluetooth on other phones.
Plus, what kind of storage will this thing use? I mean, it has to fit in a SIM card, so will there even be space for a miniSD card?