Default [Q] Interface/Controlling Android remotely via USB Rx/Tx commands

Here's some context, skip below the asterisks*** to read my actual question:

I have an arduino project I am working on that combines the arduino with GPRS, relay, and camera attachments (shields) to act as a smart alarm for a car. Essentially extending the range of functionality (remote starting, lock/unlock/ alerts etc...) to my smartphone.

Since car alarm sirens are annoying and useless, I would rather be called if my car is being "violated". The GPRS and arduino could easily handle phone call or text message notifications. It could also receive texts and turn on relays etc...

One feature I think would be great would be the ability to send a MMS message with a picture of the inside of the car. This would be difficult and probably more expensive to do (needs stronger arduino board, good camera etc...)

Then I thought why not just hack up an "old" ($50 used android phone that can take really good pics etc...) They are just built a lot better and more compact than the hack job I would end up piecing together and cost a lot less. There is only one thing I can think of... see below.

1) Is there any way to interface or control an android phone through the serial communication connector (ie usb plug hole) using commands from a device such as a raspberry pi, or arduino or similar.

What I would want to do is have a trigger (arduino monitor the dome light voltage line) to signal the arduino to control the phone to do the following:

--Call me
--take picture inside car
--send said picture via mms to me

I would also like the arduino to be able to read the sms messages I send to the phone in my car to do things like roll windows up, remote start etc... (arduino can do this last part with the gprs) as long as the arduino can read the text message it can perform something.

I am not looking for a remote client (like VM whatever its called).

If this isn't the place for this, please let me know where to start looking.