It'd likely create its own channel.
Out of what? Assuming it's, say, in a safe, buried in concrete, powered by ... sod, the power supply. Hmm.
OK, it's floating in space, powered by solar panels. It might - might - be able to hack the panels (since the power supply has to be connected to the processor) but I don't think that would let it escape.
Unless it's possible to hack reality via pure math, I don't see what resources it has to escape with. It can't order proteins over the internet to assemble a nanofatory. It can't persuade a passing human to plug in an ethernet cable. Short of black-swa...
Update 2013-09-05.
I have since played two more AI box experiments after this one, winning both.
Update 2013-12-30:
I have lost two more AI box experiments, and won two more. Current Record is 3 Wins, 3 Losses.