I recently added a Bluetooth interface for playing music from cell phones. It works great and was easy to install, so I thought I'd post the details.
There are plenty of products on the market, but this is the one I got:
Milennia MIL-BTREC Bluetooth Adapter
$40 from Crutchfield
The installation took 30 minutes start-to-finish, including removing the air conditioner duct so I could reach the wiring. My Clarion M455A head unit has two female RCA jacks for auxiliary input, so the Bluetooth device plugs right in. It uses 12-volt power, so I tapped into the wires that power the head unit. The device is 1" long and weighs only a few grams, so I just left it hanging on the back of the head unit.
Pairing the device with my iPhone was easy. Now I can sit at the helm and play music from the phone with no cables. The sound quality is as good as with a cable. The range is decent. If I walk out to the swim platform with the phone in my pocket, the signal starts breaking up, but it works great at the helm or anywhere in the cabin.
It's mildly annoying when a song gets interrupted by an email notification, but that comes with the territory. To me, that's an easy trade-off because my phone is always updated with my current music collection. The last time I played music from a CD was years ago, so the boat's 6-CD changer never gets used. Maybe I'll take it out and use the space for something else.