I created a simple UDP echo server sketch for the Spark Core. You can find the code at https://gist.github.com/blakejakopovic/cbb389998776033c2135.
“A simple UDP echo program for the Spark Core Arduino based device. You can send a single byte (ie. ‘a’) of data and have it sent back. This program serves no real practical application, but can be used to learn and tinker with UDP and inter-device communication.”
It is a little more fleshed out the the Spark Core documentation for UDP Communication, and should help to get people started using UDP. See http://docs.spark.io/#/firmware/communication-udp.
“You can test sending and receiving UDP packets using the Packet Sender application, available for Windows, Mac, Ubuntu and Andriod.”
Available for free at http://packetsender.com/