We've encountered a few mobile phones that integrate music playing and include stereo headphones that double as a hands-free headset.

FORBES: Mixing Music And Mobile Phones

Blaster Bee is a rechargeable, compact-size, on-the-go stereo speaker that plays music wirelessly from any Bluetooth device and that can double as a hands-free speakerphone, with its built-in microphone.

ENGADGET: BeeWi's Ghost Bee Bluetooth headphones also stream music to your stereo (hands-on)