APRS is a protocol for device location over RF and TCP/IP.
I'm using APRS for Windows Phone 1.1.0.0 by Stefan HB9TWS.
One operating note. If you are on the U of Michigan campus as a guest, you can connect to the Internet over the MGuest network. While on this network, APRS will appear to work, but the beacons will be silently dropped. Disconnect your phone from wifi and use your cell connection if you want to post to the APRS network.
If you're not running a Windows Phone (and most people aren't) there are clients for Android and for iPhone.
I have not used either of these recently, and there may be others.
For viewing the APRS network, I use aprs.fi , e.g.
I don't yet have an HT or 2m rig for my car that does APRS over RF, but I have my eyes open.
