A useful JME2 app for GPS datum conversion i.e NMEA WGS84 to MGRS, OSBG36, UTM, UTM 1:25000 map, decimal degrees conversion etc. Which allows cellular phone GPS with real paper maps.

http://utmdata.blogspot.com/

Also will compute lots of other useful information such as sun, moon set and rise times, moon phase and the full location data can be sent via SMS text message and load the appropriate Google map tile. (if network services are available)