Depends on the phone. Most smart phones (at least my iPhone) give you the option of which device to take the call on.
Sometimes I am driving and it is too noisy, so I switch over to the iPhone speaker from the car speaker. There is a button that pops up...or maybe its the "audio" button that shows up during a call.
PLEASE do not send questions via Private Message, my inbox fills up too quickly. Post questions in the forum as a new thread so that other users can benefit from the answers. Use Private Messages for sensitive information only (VIN, Contact info or things you do not want the public to see).