Meh. I've looked at it before. I'm either at work and have a computer or at home and with feet of an always on computer. There's just almost never a case where for some reason want a portable internet connected device. A smart phone just adds no value to my life. Certainly not $40/month worth of value.
Actually, a number of music players that are not smartphones have Bluetooth A2DP, like iPads and iPod touches:
iOS: Supported Bluetooth profiles
If you already have such devices, you can use them as a music player for your Tesla. You'll want something that supports the AAC or apt-X codecs, otherwise it will default to SBC which will sound horrible. A number of non-smartphone devices have such Bluetooth A2DP support if you are so inclined while we wait for Tesla.