You MUST tell your sales point of contact that you will be spread trading. The risk dept. will make some adjustments to your account default settings. Having said that, they will quickly take that back if you are simply letting naked legs run wild in the market. Spread trades mean offset or 'hedged' positions.
Any large, reputable Chicago FCM like RJ O'Brien, RCG, Advantage, Crossland, Kottke, etc. etc. will have a risk manager who will adjust your account default settings to accomodate intraday spreads. At Advantage, for example, they give my clients 4:1 intraday leverage before the overnight CME margins for spreads kick in.
An Introducing Broker will not know what the f*** to do typically. Deal directly with the FCM. Most IBs do not have risk systems robust enough to accomodate properly margined spread positions. From what I have seen, they typically tend to treat each leg as outright risk. Which is, of course, lazy and incorrect.