My Jabra Freeway car speakerphone retransmits on FM to the car radio, if that's what the kind of unit you're referring to. I saw your original post, but didn't reply to it because I'm not that impressed with what the Freeway does. Even though there's only a couple of feet distance between the unit and the radio there's often static, and even a distant and weak station will cause interference. You can choose any frequency, but if you're traveling you're bound to pass into and out of range of stations on the same frequency, and it's a pain to be changing frequencies all the time. The sound quality is rather poor compared to a good commercial radio station on the same radio - somewhat muffled and poor frequency response.
Having said this, I should mention that the FM part is not why I bought the Freeway. I primarily use it just for the speakerphone, and it does a very good job at that. I'm not sorry that I bought it; I'm just disappointed in the FM.