Can I use a pin/password/pattern lock and safely have basic phone functionality while in car? I would like to lock my phone with a pin for additional security.  Also, I try to minimize my phone usage in the car, but in the event that I do need to call someone, I would like to be able to do so without having to enter a pin. I would like to do this by automated means if possible. 

I see two possible directions, but there could be others


Use some third-party lockscreen app that supports pin/password/pattern while containing shortcuts to a few apps. I've seen lockscreens that have shortcuts to certain apps, but they don't provide a pin lock.
Have a Car Home app that automatically launches when I plug in the headphones.  Car Widget launches on headphone plugin, but it provides access to other screens as well, which I don't want.  It has to be headphones though, I don't have a car dock or bluetooth or even a car power cable.
There are programs like Tasker, and llama that can automate things like that for you. But the problem here is how to tell those program that you are inside your car. If the conditions were like time of day, location or battery percentage you could easily use those programs to accomplish such task.

In programs like Tasker and Llama, you can create task so that your lock screen will be disabled when you plug in headphone. But the problem here is, if anyone, anywhere plugs in the headphone your lock screen will get disabled.

Also Sony recently release NFC tag.

http://www.psfk.com/2012/01/sony-nfc-tags.html">

Maybe you can have one such device in your car and provided that you have NFC in your phone you can just tag it and the lock screen will be disabled. And maybe tag it again before leaving the car to enable the lock screen again.