An AP story on the discovery of more drug cartel radio towers in Mexico:
http://www.toledonewsnow.com/story/19671161/mexico-finds-cartel-radio-network-300-foot-tower
Rumor had it that the cartels were being supplied by radio communications dealers in Texas, but I haven't found any information to support that yet.
UPDATE:
Another interesting and more detailed story about this has appeared here:
http://www.borderlandbeat.com/2012/10/can-you-hear-me-now.html