In addition to the other topic, I have a 270EX flash. Can I use it on my T3i to act as a wireless controller, or do I have to use the built-in flash? I have some thoughts on how to test it, but does anyone have any ideas?
I don't think the 270EX has any wireless capability, either as a master or slave. That means that you'd have to use the built in flash of the T3i or purchase a speedlite with master capability if you wanted to use something more powerful on-camera, which in the current Canon Speedlite lineup means a 580 EX II.
I was kind of hoping that the camera would just pass the wireless flash bursts on to the 270EX for re-transmission, since the camera has Master capability.