as stated, since the 3300bt does not have a usb port on the rear it is possible to redirect the port to the rear by disassembling and soldering a connection to the existing one. Overall I'd call it a bigger pain in the ass than it's worth it.
I use the 4300, my main goals were to have the ability to expand to what I needed while keeping the crap like usb and aux ports off the front. Love it greatly. I did not see the need for the bt when I purchased the 4300, however as first suby stated, it is possible to get an addon for it.
Adding the bluetooth is a little bit more but you can mount the microphone where ever you want. The most common place tends to be on the steering wheel column as it is right in-front of your mouth instead of built into the headunit itself. I don't know where the 3300 mic is, but might be something to look for.
I know a few people with mics built into their headunit and I hate talking to them when they use it.