Once a niche feature, Bluetooth has exploded in a big way. The reason: stereo. A new breed of musically inclined cell phones can transmit your tunes to an ever-growing number of wireless headsets and speakers. We've tested a wide range of new options, covering the gamut from simple earbuds to powerful standalone audio systems. Before you buy, make sure your phone or media player supports the A2DP (Advanced Audio Distribution Profile) required to take full advantage of wireless music. The mighty iPhone doesn't even support this feature (at least not yet). But plenty of other handsets do, from the $25 Samsung Sync to the $199 BlackBerry Curve. Stream on.