I wasn't able to release the original code as it belonged to Facebook, but Nathan Yao wrote a great blog post covering how to do make a similar map (including code): http://flowingdata.com/2011/05/11/how-to-map-connections-wit...

To be honest, 80% of the code was getting the data into the right shape and the other 20% was a slow implementation of the great circle calculations (I didn't know about the geosphere package so I rolled my own). Nathan's code is better.