most basic ROM

[PPCFreak]

Your think this too hard.

Couple of others have done this already but using the power wires from the vibration motor to trigger the start signal.

Remote Start using Cell Phone: Part 1 | Dave Hacks

See link above.

I currently have an apache phone I was looking at doing this with but am planning to go the paid cell route and modify the way the link above talks.

Couple of issues I see with this: Need a method to authenticate the signal to start (if using SMS, any sms from any cell phone would trigger the vibrator in the phone, thus sending start signal). Using a DUMB phone would make this harder.
Using a smart phone (Apache was my thought) would allow custom code to setup the authentication code (SMS with CERTAIN text), or better option would be an REPLY from the Apache to the sending device asking ARE YOU SURE....

Just my thoughts out loud.

EDIT: Doing the door locks might be harder....doing the door locks in conjunction with the start should be a option of the remote starter so should be okay.
But door locks by themselves would be a lot more difficult, if using ONLY the vibrator motor wires from the cellphone/smartphone.

Again thoughts out loud.