Bluetooth is not just for wireless audio between your mobile phone and in-ear headset. It is being built in more and different kinds of devices, and you also can use standard peripherals to add wireless capability to existing components.
There's music packed up in your phone and MP3 player, so now you can share from your phone though Bluetooth -- and play through your PC speakers or even your hi-fi system. Or broadcast in the other direction, from your MP3 player or PC media library to listen on your phone headset.
For example, see the Sony line of Bluetooth transmitter / receiver accessories:
The Sony Ericsson MBR-100 Bluetooth Music Receiver receives music from your phone, so you can hear it though your hi-fi system ($79).
Find the Sony Ericsson MBR-100 Bluetooth Music Receiver on Amazon.com
The Sony TMR-BT10 Bluetooth transmitter module sends stereo audio from a digital music player to a Bluetooth-equipped headset, speaker system or car stereo ($79 / $53).
Find the Sony TMR-BT10 Bluetooth transmitter on Amazon.com
The Sony HWS-BTA2W Bluetooth transmitter/receiver is dual-use ($79). As a transmitter, it streams stereo audio from devices with standard stereo mini plugs, such as cell phones with adapters, MP3 players, PCs, and home stereo systems. As a receiver, it converts almost any speaker system into a stereo Bluetooth speaker from the line out jack.
Find the Sony HWS-BTA2W Bluetooth transmitter/receiver on Amazon.com
See more on Bluetooth headphones and accessories in my new article on Trends in Audio Accessories
See the Portable Audio Accessories Gallery under Wireless Transmitter / Receivers for details and related products.