quant would be ideal to get into trading especially when you get into the modeling side, but it isn't essential. I know quite a few guys in trading with comm, com/arts or com/law, majoring in finance. what is important is experience (preferably in the industry) and the ability to cope with the pressure of a trading job. At the end of the day, it's whoever brings in more money.....
besides, from what i've heard, its hard to get into a trading position but even harder to stick it out, not everyone is cut out for it and IB's often take 5-10 interns but only offer one grad position. I don't think they even take grads in prop trading, the well known UNSWer been the exception.