Yes the MPX220 does have a regular headset jack, sort of. It is 2.5mm and is not wired the same as even the SMT5600, but you can certainly find adapters to convert it properly to attach it to an aux in on a car stereo.
http://stores.ebay.com/esoTechTrix You'll need the adapter and a 3.5mm stereo plug to whatever your car takes, cable.
You will need to go the BT route on the GPS. For cabled GPS it is either a USB client, requiring the phone to be a USB host, or it is serial, and I'm not aware of any smartphone with host or serial capabilities.