The idea is an iphone case that's a wallet as well.
I have looked extensively and there are 2 main versions of this being made right now and they both suck and have poor customer reviews. The first version is a big bulky type wallet (leatherish) that your iphone fits into. It is too big and clumsy. So the young demo will never pick it up.
The second is closer - but the whole case is metal and the wallet sleeve is not flexible so the credit cards and money get stuck or are too loose. Tons of bad reviews.
Here is the first:
Michael Kors Wallet Clutch for iPhone - Apple Store (U.S.)
Here is the second:
iPhone Wallet Cases, iPhone ID Credit Card Cases for iPhone 3G/3GS at Case-mate
There is one that "snooky" is also promoting that is all rubber too - but again I dont think it works just right. It looks like something from a sex shop...
Here is what would sell... a case like the normal "incase" hard cases (or whatever) - but have an elastic pocket on the back. Then, its easy to slip a license and a credit card or some cash in there when you are going out or if your going to the gym or to the pool, etc...
You figure out a way to make one of these that keeps your phone the same small size but conveniently holds a couple of cards and a $100 bill and you are in business my friend.
So, to whomever will act upon it - good luck :-)