I use the SPH10H-FM.  While I do love the product, the problem is that while cruising at highway speed listening to the radio the incoming call beeps are very faint.  I suggest that when a call is incoming, completely cut out the radio while the beeps are going on, not just for a second or two but until the call is either accepted or missed. Also increase the volume of the beeps and perhaps change from beeps to a ringing sound that may be more distinct.