Here's how I control my worldwide team of l33t agents.
I setup an Ebay shop called hollow_volcano selling widgets and other crap. I use stegnogaphy to implant my messages into some of the shop photos. When agent-X decodes the message he uses a dead drop to get disposable_agent-Y to order some widgets.
Five blue and five red widgets means agent-X is available but five blue and five green widgets means that he is not. (other colour codes are available)