Sign up for Gmail http://mail.google.com/. Then install Video Chat plug-in http://www.google.com/talk/. This is the download on the left. You will then be able to make free outgoing phone calls to the US and Canada by going to your Gmail account and clicking on "Call Phone" next to the green phone icon on the bottom left. I don't believe that 911 calls can be made from this phone app, but you can call your police station with their regular phone number.
*For different countries, you will have to experiment with your versions. I'm not sure what's available.
All I know is the one I use is combined with access to Canada, and outgoing calls are free within this area.
ALSO...A CHARGED CELL PHONE, EVEN WITHOUT SERVICE, IS ABLE TO DIAL 911. So, if you have an old cell phone and believe you're in danger, please charge your phone and carry it with you. If you want to test 911, it's best to test it in the daytime and let them know why you are testing your phone, but keep it short so you don't tie up the 911 line.