How many unlocked iPhones (no contract) can you buy from an Apple store?
Selling unlocked phones is a fairly new thing for Apple retail. They've never been part of a product launch - so looking back, the precedent is NIL. There is great precedent for any new phone launch to have lines and quotas for the first 30 to 60 days after a product introduction. There also is precedent for a huge shipment on launch day - then limited stock for a few weeks as things sell faster than they can be made.

I would simply stop by your store and get to know the business team if you have business needs. Until the policy is announced, it should be handled like any other phone in terms of what payment is allowed (cash or not) as well as purchase limits.

The last launch, it was one phone per person while availability was limited and one web order at a time. Once the stores stopped selling out of inventory on a daily basis, it was easier to just walk in and get a phone. Last time I checked, the store has to bring out a different physical box when I purchased an unlocked phone ( I changed my mind about AT&amp;T contract half way through the process). The current stock does ship as an AT&amp;T phone or an unlocked GSM phone - they are not the same SKU. 

I suppose the computers could use a common stock and "unlock" the device when selling, but that would be different than what happens today. I do know that the iOS app to reserve product worked very well last launch, so do think about getting that installed if you are keen to get a few phones as soon as iOS 5 launches.