I was in the same position as you during early 2002. My dad was driving my car, late at night on a dark stretch of highway and had a blowout...in December...on the driver's side (which, as it happens, was the traffic-side when he pulled off the road.)

In my experience, pay as you go might not be what you want. Its been a while since I looked into it, but minutes you buy actually will expire after a while, possibly leaving you stuck.

Then I found this site:
http://www.emergencycellphones.com

To sum it up, any cellphone, activated or not, is capable of making 911 calls AND cellphone operator calls, which can get charged to a credit card at a very high per-minute rate. However, if you're expecting to talk maybe 5 minutes every couple months, the cost turns out being significantly lower than a normal cell plan.

I read up on it and bought a cellphone and charger off Ebay for something like $15. I never actually had to use it, but it did make me feel better.

(Eventually, when my sister went to college, my family boughther a real cellphone and a few months after, we decided to get 2 more with verizon's family plan, one for me and one for my mom. That was almost 2 years ago now.)