Really tiny ARM computer the size of an RJ45 socket: http://www.digi.com/products/embeddedsolutions/digiconnectmespecs.jsp

Really tiny GPS module (also contains an ARM): http://www.rfsolutions.co.uk/acatalog/GPS_Module.html

I think all you’d need to add is a power converter from POE (48V) to the 3.3V wanted by the modules.