I was wondering the same thing. Right now I've been doing spreads via the phone at one of the local Chicago houses, but was itching to move my spread trades onto something like IB. So, for example, I wanted to do old crop new crop corn spread or calendar spreads on Eurodollars or emini S&Ps on Globex, the credit will be shown on the IB platform? My spread trades tend to be in liquid markets, so is it possible to initiate both legs almost immediately (like say SP500 vs Nasdaq 100)?