I think he has a no compete deal with WWE in the US until 2010.
And by the way, anyone who has been in WWE with one or two iMPACTs is already at the top of TNA. The sad thing is that I am sure he wouldn't wrestle never in iMPACT, just like Angle.
Brock is just stupid, he practically messes his wrestling future in the US. Why don't admit it, he constantly says he wrestled in WWE for the cash and that he hated wrestling, he got out of WWE, goes to Japan to what, to wrestle, then gets his waited MMA match, and, he returns to wrestling. Why don't come back to WWE? He can't complain about the money, I am sure he got a nice paycheck, and about his character being poorly used, well, when you are 2 times champion in year and a half.