Off the record, I would have to assume that RIM and Cingular would replace the device if it is found to be defective. It would be very easy for both companies to gather a list of buyers and then send out a letter with instructions for replacement.
All I might suggest is that you not worry about paying for a device with this problem. Both Cingular and RIM will make it right. It is their reputation and neither company will want to stick users with a less than quality product.
Once RIM finds the problem and corrects it through manufacturing, we will be notified with options. All I can tell you is that this is a high priority for both companies right now.
Also keep in mind that this is NOT only afected by Cingular's devices. Rogers has the same issue.
Again, this is only my opinion. In no way am I stating something that has been told to me by either company.