Of course you're correct not to presume.
But what I meant is that a common feature on many aftermarket GPS devices is to also offer BT speakerphone/voice-dialing functions, among other functions. Recent state law changes are accelerating this. And it's part of the digital device convergence movement in which each segment is trying to assume the functions of their adjacent market competitors and in doing so, becoming the one device a consumer lives with. So I was speculating that car enthusiasts would flock to a 'one-device' that includes the functions of the product you cited, along with the other functions that popular convergence devices embody. And, consistent with the convergence patterns in the market, they are less likely to, in volume, have two devices in their car. So to drive volume adoption and sales, adding these functions is an interesting thought.
Sorry for the lengthy response, and the divergence from the thread.
I don't like to guess peoples intent.
I also don't see how allowing a phone to connect thru this device would be at all useful.