It's called APRS. Automated Packet Reporting System. Yes, you have to have your ham license. Basic setup is connect a GPS --> Interface --> Ham Radio. Based on your settings, it beacons out your position every so often. Mountain top digi-peters and i-gates pick up that signal and upload it to the internet. I'll dig up some better info on how it all works and report back.
Here's a write up of my setup as I was redoing some custom cables to work with an older GPS.
http://www.4x4ham.com/showthread.php?435-APRS-Virgil-s-Setup-11-30-2010
There are also smartphone apps, but you still need to have a ham license to use them. U2APRS is my favorite, but APRSDroid isn't bad either. Downside of these is they stop working when you lost data service. (Most trails)