We get asked a lot if you can just plug your phone or iPod directly into our amplified speakers. Although you can technically hook them up directly to your phone/ipod, you will not get full volume that way. The outputs of your phone are designed for headphones, and are made to be barely loud enough for that (thank the lawyers for that one). Usually about 1.5v output, vs. 2v for a good bluetooth adapter. This results in sound that is fairly loud and clear, but not near as loud as it would be with an external source like a Bluetooth adapter.
Another big factor is how difficult it is to adjust the volume on your phone. Our Bluetooth adapters mount nicely to the handlebars and can be adjusted while riding, even with gloves. You can put your phone in your pocket, and not risk having it bounce down the highway when you drop it while struggling the go to the next song or turn the volume up.