Your other options (which I did with Capital One - who until recently never reported limits) is to max out your credit line for a month and then pay it off. Of course that is easier to do with a $5k limit that it is with a $25k limit.

The "no preassigned limit" is really a crock. Every card (even Amex) has a limit, above-which alerts will be triggered. The bank will then review the transactions before providing approval. In addition, every card I've seen has an outstanding balance limit - for example, if you charge $22k but your limit is $20k, you have to pay down $2k before your next statement date.

I smell a class action lawsuit coming...